There is something similar to this in John, chapter 21. However, there it was a post-resurrection apparition to Simon and the other apostles near the Sea of Tiberias or Galilee, like here. However, nothing like this can be found in Mark and Matthew. Luke said that when Jesus had finished speaking (ὡς δὲ ἐπαύσατο λαλῶν), he told Simon (εἶπεν πρὸς τὸν Σίμωνα) to go out into the deep water (Ἐπανάγαγε εἰς τὸ βάθος) of the Sea of Galilee. He wanted them to let their nets into the water to catch some fish (καὶ χαλάσατε τὰ δίκτυα ὑμῶν εἰς ἄγραν). Jesus wanted them to go fishing.
This saying about causing little believing children to sin or stumble can also be found in Matthew, chapter 18:6, and Luke, chapter 17:1-2, with some minor changes. Mark indicated that Jesus said that if anyone of them caused these little ones, who believed in him, to be scandalized or stumble on a block (Καὶ ὃς δ’ ἂν σκανδαλίσῃ ἕνα τῶν μικρῶν τούτων τῶν πιστευόντων), it would be better for them (καλόν ἐστιν αὐτῷ μᾶλλον) to fasten a great heavy millstone around their necks (εἰ περίκειται μύλος ὀνικὸς περὶ τὸν τράχηλον αὐτοῦ). They should be thrown or cast into the deep sea (καὶ βέβληται εἰς τὴν θάλασσαν). Causing the believing little children to sin meant it was better for that person to die in deep water with a heavy millstone around their neck. This millstone was a stone for grinding various grains.