Mishkat al-Masabih 467

Al-Muhājir ibn Qunfudh said: ‘I came upon the Prophet while he was urinating and greeted him, but he did not return my greeting until he had performed ablution. He then explained: “I disliked mentioning Allah, Mighty and Majestic, except in a state of purity”’—or he said, ‘in a state of purification.’

Abū Dāwūd transmitted it. Al-Nasāʾī transmitted it only up to ‘until he had performed ablution,’ and added: ‘When he had performed ablution, he returned the greeting.’