Musannaf Ibn Abi Shayba 1:674

Waki’ narrated to us, from Sufyan, from Mansur, from Salim ibn Abi al-Ja’d, from Salim ibn Abdullah ibn Umar, from his father, who said: When the person in a state of major ritual impurity (junub) wants to eat, drink, or sleep, he should perform ablution (wudu).