We've not got evidence for this, what we have is the first known dates that these texts were accounted; yet there is always a possibility that these were passed down from the time of Yeshua.
Composed AFTER the letters of Paul, Mark and Matthew were INTENDED as symbolic fiction, being written in a symbolic chiastic structure.
Only with Luke-Acts did Christians start to view the four Gospels literally.
The sayings of Jesus in the Gospels are things Paul originally said. See Nikolaus Walter's ‘Paul and the Early Christian Jesus-Tradition’.
The events in Mark and Matthew are based on the LXX, directly borrowing its language:
The Donkey(s) - Jesus riding on a donkey is from Zechariah 9.
Mark has Jesus sit on a young donkey that he had his disciples fetch for him (Mark 11.1-10).
Matthew changes the story so the disciples instead fetch TWO donkeys, not only the young donkey of Mark but also his mother. Jesus rides into Jerusalem on both donkeys at the same time (Matthew 21.1-9). Matthew wanted the story to better match the literal reading of Zechariah 9.9. Matthew even actually quotes part of Zech. 9.9.
The Sermon on the Mount - The Sermon of the Mount relies extensively on the Greek text of Deuteronomy and Leviticus especially, and in key places on other texts. For example, the section on turning the other cheek and other aspects of legal pacifism (Mt. 5.38-42) has been redacted from the Greek text of Isaiah 50.6-9.
The clearing of the temple - The cleansing of the temple as a fictional scene has its primary inspiration from an ancient faulty translation of Zech. 14.21 which changed 'Canaanites' to 'traders'.
When Jesus clears the temple he quotes Jer. 7.11 (in Mk 11.17). Jeremiah and Jesus both enter the temple (Jer. 7.1-2; Mk 11.15), make the same accusation against the corruption of the temple cult (Jeremiah quoting a revelation from the Lord, Jesus quoting Jeremiah), and predict the destruction of the temple (Jer. 7.12-14; Mk 14.57-58; 15.29).
The Crucifixion - The whole concept of a crucifixion of God’s chosen one arranged and witnessed by Jews comes from Psalm 22.16, where ‘the synagogue of the wicked has surrounded me and pierced my hands and feet’. The casting of lots is Psalm 22.18. The people who blasphemed Jesus while shaking their heads is Psalm 22.7-8. The line ‘My God, my God, why have you forsaken me?’ is Psalm 22.1.
The Resurrection - Jesus was known as the ‘firstfruits’ of the resurrection that would occur to all believers (1 Cor. 15.20-23). The Torah commands that the Day of Firstfruits take place the day after the first Sabbath following the Passover (Lev. 23.5, 10-11). In other words, on a Sunday. Mark has Jesus rise on Sunday, the firstftuits of the resurrected, symbolically on the very Day of Firstfruits itself.
Barabbas - This is the Yom Kippur ceremony of Leviticus 16 and Mishnah tractate Yoma: two ‘identical’ goats were chosen each year, and one was released into the wild containing the sins of Israel (which was eventually killed by being pushed over a cliff), while the other’s blood was shed to atone for those sins. Barabbas means ‘Son of the Father’ in Aramaic, and we know Jesus was deliberately styled the ‘Son of the Father’ himself. So we have two sons of the father; one is released into the wild mob containing the sins of Israel (murder and rebellion), while the other is sacrificed so his blood may atone for the sins of Israel—the one who is released bears those sins literally; the other, figuratively. Adding weight to this conclusion is manuscript evidence that the story originally had the name ‘Jesus Barabbas’. Thus we really had two men called ‘Jesus Son of the Father’.
Last Supper - This is derived from a LXX-based passage in Paul's letters. Paul said he received the Last Supper info directly from Jesus himself, which indicates a dream. 1 Cor. 11:23 says
"For I received from the Lord that which I also delivered to you, that the Lord Jesus in the night in which He was betrayed took bread." Translations often use "betrayed", but in fact the word
paradidomi means simply ‘hand over, deliver’. The notion derives from Isaiah 53.12, which in the Septuagint uses exactly the same word of the servant offered up to atone for everyone’s sins. Paul is adapting the Passover meal. Exodus 12.7-14 is much of the basis of Paul’s Eucharist account: the element of it all occurring ‘in the night’ (vv. 8, 12, using the same phrase in the Septuagint, en te nukti, that Paul employs), a ritual of ‘remembrance’ securing the performer’s salvation (vv. 13-14), the role of blood and flesh (including the staining of a cross with blood, an ancient door lintel forming a double cross), the breaking of bread, and the death of the firstborn—only Jesus reverses this last element: instead of the ritual saving its performers from the death of their firstborn, the death of God’s firstborn saves its performers from their own death. Jesus is thus imagined here as creating a new Passover ritual to replace the old one, which accomplishes for Christians what the Passover ritual accomplished for the Jews. There are connections with Psalm 119, where God’s ‘servant’ will remember God and his laws ‘in the night’ (119.49-56) as the wicked abuse him. The Gospels take Paul's wording and insert disciples of Jesus.
Refs:
(1) John Dominic Crossan, The Power of Parable: How Fiction by Jesus Became Fiction about Jesus (New York: HarperOne, 2012); (2) Randel Helms, Gospel Fictions (Amherst, NY: Prometheus Books, 1988); (3) Dennis MacDonald, The Homeric Epics and the Gospel of Mark (New Haven, CT: Yale University Press, 2000); (4) Thomas Thompson, The Messiah Myth: The Near Eastern Roots of Jesus and David (New York: Basic Books, 2005); and (5) Thomas Brodie, The Birthing of the New Testament: The Intertextual Development of the New Testament Writings (Sheffield: Sheffield Phoenix Press, 2004).
