Purification (Kitab Al-Taharah)

Dawud :: Book 1 : Hadith 17

Narrated Muhajir ibn Qunfudh:

Muhajir came to the Prophet (peace_be_upon_him) while he was urinating. He saluted him. The Prophet (peace_be_upon_him) did not return the salutation to him until he performed ablution. He then apologised to him, saying: I disliked remembering Allah except in the state of purification.