Abd al-Rahman bin Yazid (may Allah have mercy on him) said: We were with Sayyiduna Salman (may Allah be pleased with him) on a journey. He went apart from the people and relieved himself, then came back. We said to him: O Abu Abdullah! Perform ablution, perhaps we will ask you about some verses of the Qur'an. He said: "Ask, for I am not touching it, and 'None touch it except the purified' [Surah al-Waqi'ah: 79]." So we asked him, and he recited the Qur'an to us before performing ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 422