It was narrated from Al-Muhajir bin Qunfudh that he greeted the Prophet (ﷺ) with Salam while he was urinating, and he did not return the greeting until he had performed Wudu'. When he had performed Wudu' he returned the greeting.
Hadith ReferenceSunan an-Nasa'i / Mention The Fitrah (The Natural Inclination Of Man) / Hadith: 38
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:ضعيف، إسناده ضعيف، ابو داود (17) ابن ماجه (350) انوار الصحيفه، صفحه نمبر 321