Luke 9:14

For they were about five thousand men. And he said to his disciples, Make them sit down by fifties in a company.

Cross-reference

Mark 6:39 adds that Jesus commanded them to sit on green grass—Luke's account here specifies groups of fifty, both describe seating.

Mark 6:40 records they sat in groups of hundreds and fifties—Luke's account here mentions groups of about fifty, a consistent detail.

Matthew 14:19 includes Jesus blessing and breaking the loaves—Luke's account here only has the seating command, Matthew fills in the blessing.

John 6:10 adds the detail of much grass and the number, providing a fuller account of the same command to sit down.