Musannaf Ibn Abi Shayba 1:1100

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, from Abd al-Rahman ibn Yazid, who said: We were with Salman on an errand, and he went and relieved himself. Then he returned, and we said to him: "Perform ablution, O Abu Abd Allah, perhaps we may ask you about verses from the Quran." He said: "Ask, for I do not touch it; indeed, none touch it except the purified." He said: So we asked him, and he recited to us before he performed ablution.