Acts 20:35 In everything I did, I showed you that by this kind of hard work we must help the weak, remembering the words the Lord Jesus himself said: 'It is more blessed to give than to receive.'"
Critics may doubt the correctness of this passage, accusing Paul of manufacturing a "nonquote" of Jesus because it is not found in the Gospels as said by Jesus. But we may not suppose that the Gospels contain all that Jesus said. This and a few other floating traditions are called agrapha, though this is the only one with any solid literary attestation from the time period in question.
One critic responded to a letter-writer who makes the same point by saying:
I have no objection to this comment as long as you agree to the following. First, all who hear this verse are told that nowhere in the Bible did Jesus make this statement. Deception is quite common with this verse. Secondly, Paul could not have heard this statement himself, since he circulated when Jesus was no longer present. At best, Paul is quoting hearsay. Thirdly, there is no evidence, whatever, that Jesus ever made the statement. All we have is Paul's word. Where did I claim that "only statements of Jesus contained in this invalid source can be used by Paul"? Paul can quote Jesus anytime he desires. As long as he or his followers don't attempt to give people the impression that alleged quotes from Jesus, such as that found in Acts 20:35, are supported by Scripture, there is no problem.
To call what Paul says "hearsay" requires qualification. By modern, legal definition it may be "hearsay" but this hardly makes it inaccurate, especially in light of rabbinic and didactic teaching techniques that would have ensured the basic transmissional accuracy of the words of Jesus, as well as exercised control upon words attributed to him.
This was the norm for ancient oral transmission; those who doubt will have to deal with the works of scholars of oral tradition, like Vansina and Lord, to refute this, and consider the legal definition of hearsay as well; see link below).
But what is the problem even so? Is the critic accusing Paul (or Luke) of simply making up words of Jesus? Where is his justification for this assertion, if that is what is being implied? Who has "deceived" who with this verse, and how? This seems to be nothing but an attempt to make this sound like an objection worthy of consideration. It is never explained why this cannot be an authentic word of Jesus simply not recorded in the Gospels.