A man passed by the Prophet ﷺ while he was urinating and greeted him with salam, but he did not return the greeting.
حدثنا عثمان وأبو بكر ابنا أبي شيبة قالا حدثنا عمر بن سعد عن سفيان عن الضحاك بن عثمان عن نافع
مر رجل على النبي ﷺ وهو يبول فسلم عليه فلم يرد عليه
Muslim narrated it in the Book of Menstruation, Chapter on Tayammum, no. 370, from the hadith of Sufyan Thawri through this same chain. Tirmidhi also narrated it, no. 90, as did Nasai, no. 37, and Ibn Majah, no. 353. It is also found in Musannaf Ibn Abu Shayba, 8/435.