I have heard this over and over and over now lets consult three irrefutable jewish sources.
According to the Jewish Encyclopedia, Encyclopedia Judaica and the Talmud, among the Jews in Israel before and during the time of Jesus was a belief in a place of everlasting torment of the wicked and they called it both sheol and gehinnom.
Disclaimer: There were different groups within Judaism; Sadducees, Pharisees, Essenes etc. and there were different beliefs about resurrection, hell etc. I am addressing only the belief stated above, Any other beliefs are not relevant to this response.
Jewish Encyclopedia, Gehenna
The place where children were sacrificed to the god Moloch … in the "valley of the son of Hinnom," to the south of Jerusalem (Josh. xv. 8, passim; II Kings xxiii. 10; Jer. ii. 23; vii. 31-32; xix. 6, 13-14). … the valley was deemed to be accursed, and "Gehenna" therefore soon became a figurative equivalent for "hell." Hell, like paradise, was created by God (Sotah 22a);
Note, this is according to the ancient Jews, long before the Christian era, NOT any supposed bias of Christian translators.
(I)n general …sinners go to hell immediately after their death. The famous teacher Johanan b. Zakkai wept before his death because he did not know whether he would go to paradise or to hell (Ber. 28b). The pious go to paradise, and sinners to hell (B.M. 83b).
But as regards the heretics, etc., and Jeroboam, Nebat's son, hell shall pass away, but they shall not pass away" (R. H. 17a; comp. Shab. 33b). All that descend into Gehenna shall come up again, with the exception of three classes of men: those who have committed adultery, or shamed their neighbors, or vilified them (B. M. 58b).[/i]
… heretics and the Roman oppressors go to Gehenna, and the same fate awaits the Persians, the oppressors of the Babylonian Jews (Ber. 8b). When Nebuchadnezzar descended into hell, [ שׁאול /Sheol]] all its inhabitants were afraid that he was coming to rule over them (Shab. 149a; comp. Isa. xiv. 9-10). The Book of Enoch also says that it is chiefly the heathen who are to be cast into the fiery pool on the Day of Judgment (x. 6, xci. 9, et al). "The Lord, the Almighty, will punish them on the Day of Judgment by putting fire and worms into their flesh, so that they cry out with pain unto all eternity" (Judith xvi. 17). The sinners in Gehenna will be filled with pain when God puts back the souls into the dead bodies on the Day of Judgment, according to Isa. xxxiii. 11 (Sanh. 108b).
Link:Jewish Encyclopedia Online
Encyclopedia Judaica:
Gehinnom (Heb. גֵּי בֶן־הִנֹּם, גֵּי בְנֵי הִנֹּם, גֵּיא בֶן־הִנֹּם, גֵּיא הִנֹּם; Gr. Γέεννα; "Valley of Ben-Hinnom, Valley of [the Son (s) of] Hinnom," Gehenna), a valley south of Jerusalem on one of the borders between the territories of Judah and Benjamin, between the Valley of *Rephaim and *En-Rogel (Josh. 15:8; 18:16). It is identified with Wadi er-Rababi.
During the time of the Monarchy, Gehinnom, at a place called Topheth, was the site of a cult which involved the burning of children (II Kings 23:10; Jer. 7:31; 32:35 et al.; see *Moloch). Jeremiah repeatedly condemned this cult and predicted that on its account Topheth and the Valley of the Son of Hinnom would be called the Valley of the "Slaughter" (Jer. 19:5–6).
In Judaism the name Gehinnom is generally used as an appellation of the place of torment reserved for the wicked after death. The New Testament used the Greek form Gehenna in the same sense.
Gehinnom
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Talmud -Tractate Rosh Hashanah Chapter 1.
The school of Hillel says: . . . but as for Minim, [follower of Jesus] informers and disbelievers, who deny the Torah, or Resurrection, or separate themselves from the congregation, or who inspire their fellowmen with dread of them, or who sin and cause others to sin, as did Jeroboam the son of Nebat and his followers, they all descend to Gehenna, and are judged there from generation to generation, as it is said [Isa. lxvi. 24]: "And they shall go forth and look upon the carcases of the men who have transgressed against Me; for their worm shall not die, neither shall their fire be quenched." Even when Gehenna will be destroyed, they will not be consumed, as it is written [Psalms, xlix. 15]: "And their forms wasteth away in the nether world," which the sages comment upon to mean that their forms shall endure even when the grave is no more. Concerning them Hannah says [I Sam. ii. 10]: "The adversaries of the Lord shall be broken to pieces."
Link:Tract Rosh Hashana: Chapter I.
When Jesus taught about,
• “Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:” Matthew 25:41
• "these shall go away into eternal punishment, Matthew 25:46"
• "the fire of hell where the fire is not quenched and the worm does not die, Mark 9:43-48"
• "cast into a fiery furnace where there will be wailing and gnashing of teeth,” Matthew 13:42, Matthew 13:50
• “But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.” Matthew 18:6
• “And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.” Matthew 7:23
• “woe unto that man by whom the Son of man is betrayed! it had been good for that man if he had not been born. ” Matthew 26:24
These teachings tacitly reaffirmed and sanctioned the existing Jewish view of eternal hell, outlined above. In Matt. 18:6, 26:24, see above, Jesus teaches that there is a fate worse than death or nonexistence. A fate worse than death is also mentioned in Hebrews 10:28-31.
Heb 10:28 He that despised Moses' law died without mercy under two or three witnesses:
29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?
30 For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people.
31 It is a fearful thing to fall into the hands of the living God.
Jesus is quoted as using the word death 17 times in the gospels, if He wanted to say eternal death in Matt 25:46, that is what He would have said but He didn’t, He said “eternal punishment.” The Sadducees did not believe in the resurrection, they knew that everybody died; rich, poor, young, old, good, bad, men, women, children, infants and knew that it had nothing to do with punishment and was permanent. When Jesus taught “eternal punishment” they would not have understood it as death, it would have meant something worse to them.
…..Jesus knew what the Jews, believed about hell. If the Jews were wrong, when Jesus taught about man’s eternal fate, such as eternal punishment, He would have corrected them. Jesus did not correct them, thus their teaching on hell must have been correct.
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The traditional explanation that a burning rubbish heap in the Valley of Hinnom south of Jerusalem gave rise to the idea of a fiery Gehenna of judgment is attributed to Rabbi David Kimhi's commentary on Psalm 27:13 (ca. A.D. 1200). He maintained that in this loathsome valley fires were kept burning perpetually to consume the filth and cadavers thrown into it. However, Strack and Billerbeck state that there is neither archaeological nor literary evidence in support of this claim, in either the earlier intertestamental or the later rabbinic sources (Hermann L. Strack and Paul Billerbeck, Kommentar zum Neuen Testament aus Talmud and Midrasch, 5 vols. [Munich: Beck, 1922-56], 4:2:1030). Also a more recent author holds a similar view (Lloyd R. Bailey, "Gehenna: The Topography of Hell," Biblical Archeologist 49 [1986]: 189.
Source, Bibliotheca Sacra / July–September 1992
Scharen: Gehenna in the Synoptics Pt. 1
Note there is no “archaeological nor literary evidence in support of this claim, [that Gehenna was ever used as a garbage dump] in either the earlier intertestamental or the later rabbinic sources” If Gehenna was ever used as a garbage dump there should be broken pottery, tools, utensils, bones, etc. but there is no such evidence.
“Gehenna is presented as diametrically opposed to ‘life’: it is better to enter life than to go to Gehenna. . .It is common practice, both in scholarly and less technical works, to associate the description of Gehenna with the supposedly contemporary garbage dump in the valley of Hinnom. This association often leads scholars to emphasize the destructive aspects of the judgment here depicted: fire burns until the object is completely consumed. Two particular problems may be noted in connection with this approach. First, there is no convincing evidence in the primary sources for the existence of a fiery rubbish dump in this location (in any case, a thorough investigation would be appreciated). Secondly, the significant background to this passage more probably lies in Jesus’ allusion to Isaiah 66:24.”
(“The Duration of Divine Judgment in the New Testament” in The Reader Must Understand edited by K. Brower and M. W. Ellion, p. 223, emphasis mine)
G. R. Beasley-Murray in Jesus and the Kingdom of God:
“Ge-Hinnom (Aramaic Ge-hinnam, hence the Greek Geenna), ‘The Valley of Hinnom,’ lay south of Jerusalem, immediately outside its walls. The notion, still referred to by some commentators, that the city’s rubbish was burned in this valley, has no further basis than a statement by the Jewish scholar Kimchi (sic) made about A.D. 1200; it is not attested in any ancient source.” (p. 376n.92)
The Burning Garbage Dump of Gehenna is a myth - Archaeology, Biblical History & Textual Criticism