Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 90
Narated By Thawban : The Messenger of Allah (pbuh) said: Three things one is not allowed to do: supplicating Allah specifically for himself and ignoring others while leading people in prayer; if he did so, he deceived them; looking inside a house before taking permission: if he did so, it is as if he entered the house, saying prayer while one is feeling the call of nature until one eases oneself.