Albert Barnes Commentary Luke 5:17

"And it came to pass on one of those days, that he was teaching; and there were Pharisees and doctors of the law sitting by, who were come out of every village of Galilee and Judaea and Jerusalem: and the power of the Lord was with him to heal." — Luke 5:17 (ASV)

See this passage explained in Barnes "Matthew 9:1" through Matthew 9:7.

On a certain day. The time and place are not particularly mentioned here, but from Matthew 9:1 it seems it was at Capernaum.