Musannaf Ibn Abi Shayba 3:5108

Waki’ narrated to us, he said: Isra’il narrated to us, from Mujahid, regarding a man who finds a louse during prayer. Isra’il narrated to us, from Jabir, from ‘Amir, regarding a man who finds a louse during prayer, he said: He should leave it.