Luke, chapter 5:33, and Matthew, chapter 9:14, are similar to Mark, so that Mark might be the source of this incident, although there are some differences. Matthew had only the disciples of John the Baptist ask about fasting. Mark has this strange combination of the disciples of John the Baptist with the Pharisees who agreed about fasting (Καὶ ἦσαν οἱ μαθηταὶ Ἰωάνου καὶ οἱ Φαρισαῖοι νηστεύοντες). They wanted to know why the disciples of Jesus did not fast. The disciples of John seemed to be on the side of the Pharisees, and not followers of Jesus, as they wondered why they and the disciples of the Pharisees were often fasting or abstaining from food (καὶ ἔρχονται καὶ λέγουσιν αὐτῷ Διὰ τί οἱ μαθηταὶ Ἰωάνου καὶ οἱ μαθηταὶ τῶν Φαρισαίων νηστεύουσιν), while the disciples of Jesus were not fasting (οἱ δὲ σοὶ μαθηταί οὐ νηστεύουσιν). Some have traced the descendant followers of John the Baptist to the Mandaeans along the Iraq-Iran border.
There is something similar to this in Mark, chapter 7:2-5 and Luke chapter 11:39. These Pharisees wanted to know why the disciples of Jesus (Διὰ τί οἱ μαθηταί σου) did not wash their hands before they ate bread (οὐ γὰρ νίπτονται τὰς χεῖρας ὅταν ἄρτον ἐσθίωσιν). They said that this action was a transgression or violation against the tradition of the elders (παραβαίνουσιν τὴν παράδοσιν τῶν πρεσβυτέρων). Originally, this practice of washing hands before eating was what the Levites did in the Temple to practice ritual purity as indicated in Exodus, chapter 30:17-21. Yahweh had told Moses that there should be a bronze basin with a bronze stand for washing. Thus, Aaron and his sons should wash their hands and feet when they went into the meeting tent or the altar. The penalty for not washing your hands and feet was death under this perpetual ordinance. However, the Pharisaic oral tradition, or the tradition of the elders, had extended this practice to individual homes.
Matthew has the Pharisees react to the disciples of Jesus plucking and eating grain on the Sabbath. This is similar to Mark, chapter 2:24, at the beginning of Jesus’ ministry. It is also the same as Luke, chapter 6:2. Deuteronomy, chapter 25:24-25 stated that it was okay to pluck the ears with your hand, but you could not put a sickle to your neighbor’s standing grain or carry it away in a container. However, Exodus, chapter 34:21, explicitly said that you could not harvest grain on the Sabbath but did not mention hand picking. Thus, the Pharisees saw what had happened (οἱ δὲ Φαρισαῖοι ἰδόντες). They said to Jesus (εἶπαν αὐτῷ) that his disciples were doing unlawful things on the Sabbath by plucking and eating the grain (Ἰδοὺ οἱ μαθηταί σου ποιοῦσιν ὃ οὐκ ἔξεστιν ποιεῖν ἐν σαββάτῳ).
This response of Jesus is almost the same as in Mark, chapter 2:18, and Luke, chapter 5:33. The disciples of John the Baptist showed up here as in Mark and Luke, wanting to know why the disciples of Jesus did not fast. These disciples of John came to Jesus (Τότε προσέρχονται αὐτῷ οἱ μαθηταὶ Ἰωάνου) since John was in jail. They seemed to be on the side of the Pharisees, and not followers of Jesus, as they wondered why they and the Pharisees were often fasting or abstaining from food (λέγοντες Διὰ τί ἡμεῖς καὶ οἱ Φαρισαῖοι νηστεύομεν), while the disciples of Jesus were not fasting (οἱ δὲ μαθηταί σου οὐ νηστεύουσιν).