It is not a tradition; but a Tradition, a teaching from Christ, practiced from the beginnings of Christianity. We see in the scriptures that we are to be buried with Christ in baptism. What is not clear is the method.
"Do you not know that all of us who have been baptized into Christ Jesus
have been baptized into his death,
so that as Christ was raised from the dead by the glory of the Father,
we too might walk in newness of life"
(Rom 6:3-4)
St. Justin the Martyr (born at the end of the first century), makes reference to the triple immersion:
I shall now explain our method of dedicating ourselves to God after we have been created anew through Christ... . All who accept and believe as true the things taught and said by us, and who undertake to have the power to live accordingly, are taught to pray and entreat God, fasting, for the forgiveness of their former sins, while we join in their prayer and fasting. Then we bring them to a place where there is water, where they are regenerated in the same way as we were: for they then make their ablution in the water in the Name of God the Father and Lord of all, and of our Saviour Jesus Christ, and of the Holy Spirit.
Augustine:
"Rightly were you dipped three times, since you were baptized in the name of the Trinity. Rightly were you dipped three times, because you were baptized in the name of Jesus Christ, Who on the third day rose again from the dead. For that thrice repeated immersion reproduces the burial of the Lord by which you were buried with Christ in Baptism."
St. Cyril:
"Thus, with the help of these signs you have represented the three-day burial of Christ because, as our Saviour was in the heart of the earth three days and three nights, so in the first coming up from the water you symbolized the first day of His sojourn under the earth, and through your immersion, you symbolized the night. For, as one who walks in the night sees nothing, and he who walks during the day does so in light, so you, having immersed yourself in water saw nothing, as if you saw nothing in the night, and having come forth from the water, you see everything as in daylight. You were both dead and then born. So the salvific water was for you both a coffin and a mother. Although we neither actually die, nor get buried, nor are we nailed to the cross, but only simulate this symbolically, we, however, do indeed achieve salvation. Christ was truly crucified, truly buried, and truly resurrected. He granted all this to us, so that we, in imitating His passions, would become partakers of them and indeed would achieve salvation.
St. Basil:
To signify this death and to enlighten the baptized by transmitting to them knowledge of God, the great sacrament of baptism is administered by means of a triple immersion and the invocation of each of the three divine Persons. Whatever grace there is in the water comes not from its own nature but from the presence of the Spirit, since
baptism is not a cleansing of the body, but a pledge made to God from a clear conscience
God Bless