Abd al-Rahman bin Yazid (may Allah have mercy on him) said: We were with Salman (may Allah be pleased with him); he came back after relieving himself, and I said: "O Abu Abdullah! If only you had performed ablution, perhaps we would ask you about some verses." He said: "I am not touching it (the Qur'an)." Then he said: "None touch it except the purified" [Surah al-Waqi'ah: 79]. Then he recited to us whatever we wished.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 412