Mua'dh bin Mua'dh bin Nsr معاذ بن معاذ بن نصر · The Book of Purification

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.