Albert Barnes Commentary 2 Kings 7:9

"Then they said one to another, We do not well; this day is a day of good tidings, and we hold our peace: if we tarry till the morning light, punishment will overtake us; now therefore come, let us go and tell the king`s household." — 2 Kings 7:9 (ASV)

The lepers began to think that if they kept this important matter secret throughout the night for their own private advantage, when morning came they would be found out, accused, and punished.