When Joshua fell upon his face during Israel's defeat at Ai, God told him to rise and sanctify the people. This instruction is found in Joshua 7:10-13 (RSV):
"10 The Lord said to Joshua, “Arise, why have you thus fallen upon your face? 11 Israel has sinned; they have transgressed my covenant which I commanded them; they have taken some of the devoted things; they have stolen, and lied, and put them among their own stuff. 12 Therefore the people of Israel cannot stand before their enemies; they turn their backs before their enemies, because they have become a thing for destruction. I will be with you no more, unless you destroy the devoted things from among you. 13 Up, sanctify the people, and say, ‘Sanctify yourselves for tomorrow; for thus says the Lord, God of Israel, “There are devoted things in the midst of you, O Israel; you cannot stand before your enemies, until you take away the devoted things from among you.”