Augustine of Hippo
Catena Aurea · Johannesevangelium 6
When Jesus therefore perceived that they would come and take him by force, to make him a king, he departed again into a mountain himself alone. And when even was now come, his disciples went down unto the sea, And entered into a ship, and went over the sea toward Capernaum. And it was now dark, and Jesus was not come to them. And the sea arose by reason of a great wind that blew. So when they had rowed about five and twenty or thirty furlongs, they see Jesus walking on the sea, and drawing nigh unto the ship: and they were afraid. But he saith unto them, It is I; be not afraid. Then they willingly received him into the ship: and immediately the ship was at the land whither they went.
Mark’s1 account does not contradict this. He says indeed that our Lord told the disciples first to enter the ship, and go before Him over the sea, while He dismissed the crowds, and that when the crowd was dismissed, He went up alone into the mountain to pray: while John places His going up alone in the mountain first, and then says, And when even was now come, His disciples went down unto the sea. But it is easy to see that John relates that as done afterwards by the disciples, which our Lord had ordered before His departure to the mountain.