Muhammad replaced the Law with his own. Muhammad did not follow the OT he created his own laws. Take the law of theft, in the OT it was:
Exo 22:1 If a man shall steal an ox, or a sheep, and kill it, or sell it; he shall restore five oxen for an ox, and four sheep for a sheep.
In the OT the thief had to restore (with extra) what he had stolen. But Muhammad changed that law to:
Quran 5:38 As to the thief, male or female, cut off his or her hands: a punishment by way of example, from Allah, for their crime: and Allah is Exalted in power.
The OT law makes more sense, it adds a penalty but does not harm the person. Muhammad’s law is massively more strict.
There is also no law like the following in the Bible. The Quran’s law on marriage is clearly evil.
Sahih International (Quran 4:34): Men are in charge of women by [right of] what Allah has given one over the other and what they spend [for maintenance] from their wealth. So righteous women are devoutly obedient, guarding in [the husband's] absence what Allah would have them guard. But those [wives] from whom you fear arrogance - [first] advise them; [then if they persist], forsake them in bed; and [finally], strike them. But if they obey you [once more], seek no means against them. Indeed, Allah is ever Exalted and Grand.
Pickthall (Quran 4:34): Men are in charge of women, because Allah hath made the one of them to excel the other, and because they spend of their property (for the support of women). So good women are the obedient, guarding in secret that which Allah hath guarded. As for those from whom ye fear rebellion, admonish them and banish them to beds apart, and scourge them. Then if they obey you, seek not a way against them. Lo! Allah is ever High, Exalted, Great.
The above is not in the Bible, it is not a truth. The way Muhammad treated people is also contrary to Jesus teaching to "love one another".
Matthew 5:43-44 You have heard people say, "Love your neighbors and hate your enemies." But I tell you to love your enemies and pray for anyone who mistreats you.
Mark 12:30-31 And you are to have love for the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength. The second is this, Have love for your neighbour as for yourself. There is no other law greater than these.
As we see from the Hadith Muhammad did not love his enemies, he treated them with distain and cruelty.
7.623 Narrated Anas bin Malik: [initial text]…. When this news reached the Prophet he sent in their pursuit (and they were caught and brought). The Prophet ordered that their eyes be branded with heated iron bars and their hands be cut off, and they were left at Al−Harra till they died in that state. - Abram, Simon. Islamic Hadith . Kindle Edition.