The Muslim Challenge:
Christians, how do you confirm those words in the Bible are the words of Jesus and not words put into his mouth?
Muslims trust the words of Prophet Muhammad pbuh because we have authentic sources to prove :
1) Muhammad pbuh is a true prophet (he never lied, the testimony of people who knew him since he was a child, the miracles he performed, his character, the prophecies that came true during his lifetime etc)
2) since we believe he’s a true prophet, then all revelations are from God Almighty, the Creator of this universe
3) therefore the words in the Quran are God’s words and the words in authentic hadith are the Prophet’s words
4) the Quran is the verbatim word of God, never tampered with by human hands
How about you?
The answer to your question as to how we know the words of Jesus in the Bible are His words and “not words put into his mouth” is given in John 7:46,
Joh 7:25 Then said some of them of Jerusalem, Is not this he, whom they seek to kill?
Joh 7:26 But, lo, he speaketh boldly, and they say nothing unto him. Do the rulers know indeed that this is the very Christ?
Joh 7:31 And many of the people believed on him, and said, When Christ cometh, will he do more miracles than these which this man hath done?
Joh 7:32 The Pharisees heard that the people murmured such things concerning him; and the Pharisees and the chief priests sent officers to take him.
Joh 7:45 Then came the officers to the chief priests and Pharisees; and they said unto them, Why have ye not brought him?
Joh 7:46 The officers answered, Never man spake like this man.
Jesus Himself anticipated this very question when He responded to the question posed by the Jews who heard Him:
Joh 7:15 And the Jews marvelled, saying, How knoweth this man letters, having never learned?
Joh 7:16 Jesus answered them, and said, My doctrine is not mine, but his that sent me.
Joh 7:17 If any man will do his will, he shall know of the doctrine, whether it be of God, or whether I speak of myself.
Jesus gave another clue that reveals a very practical test of the truth of His words in the following chapter of John:
Joh 8:30 As he spake these words, many believed on him.
Joh 8:31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed;
Joh 8:32 And ye shall know the truth, and the truth shall make you free.
Only the words of Jesus produce this effect in the lives of those who continue to hear His Word and continue to believe Him!