It is narrated from Sayyiduna Muhajir bin Qunfudh bin ‘Amr bin Jud‘an (may Allah be pleased with him) that he came to the Prophet Muhammad (peace and blessings be upon him) while he was performing ablution. He greeted the Prophet with salam, but the Messenger of Allah (peace and blessings be upon him) did not reply to his salam until he had completed his ablution (and then replied to the salam). He apologized for this and said: "I disliked mentioning Allah without being in a state of purity." Hasan al-Basri (may Allah have mercy on him) used to act according to this hadith, that is, he would reply to salam only when in a state of ablution.