Some critics assert a contradiction between Matthew and Luke by point out that some of the same teachings found in the Sermon on the Mount (Matthew 5-7) are found in different contexts in Luke. For example, when Jesus offers the model prayer often known as the “Lord’s Prayer,” Matthew has Jesus teaching the multitude how to pray (Matt. 6:6-13). Luke records another instance (Luke 11:1-4), where the disciples ask Him to teach them to pray, which He does in much the same way He taught the crowd in Matthew. There is certainly no logical conflict here at all. Jesus can (and did) teach the same thing more than once.
It is worth noting that, even in Matthew’s Sermon on the Mount, strictly speaking, Jesus was actually teaching the Lord’s Prayer (as with the rest of the sermon) specifically to His disciples rather than the larger multitude. Verse one mentions the crowds but then says that Jesus went up on a mountain and “His disciples came to Him,” (Matt. 5:1) and he “began teaching them [i.e., the disciples],” (Matt. 5:2). Thus, in both cases, Jesus is actually teaching these things to His disciples. Still, we need not force the two instances to be the same. Jesus taught the same things more than once. Why would we think He would do otherwise?