´It was narrated that Ibn 'Umar said:` "A man passed by the Prophet while he was urinating and greeted him with the Salam, and he did not return the greeting."
Hadith ReferenceSunan Ibn Majah / The Book of Purification and its Sunnah / Hadith: 353
Hadith Gradingالألبانی:حسن صحيح | زبیر علی زئی:صحيح مسلم