Musannaf Ibn Abi Shayba 33:1149

Sa'id ibn Sharhabil narrated to us, he said: Layth ibn Sa'd informed us, from 'Uqayl, from Ibn Shihab, who said: I sat one day with Abu Idris al-Khawlani while he was narrating. He said: "Shall I not inform you of who had the purest food of all people?" When he saw that the people had looked toward him, he said: "Indeed, Yahya ibn Zakariyya had the purest food of all people. He would only eat with the wild animals, disliking to mix with people in their livelihoods."