Mishkat al-Masabih #434

Al-Muhajir b. Qunfudh said that he came upon the Prophet when he was passing water and saluted him, but he did not respond to the salutation till he had performed ablution. He then made his excuse to him saying, “I dislike mentioning God's name except when I am in a state of purity.” Abu Dawud transmitted it. Nasa’i transmitted it up to “till he had performed ablution” and said, “then when he had performed ablution he responded to it.”