Musnad Abu Ya'la al-Mawsili 6:50

Bishr ibn Hilal al-Sawwaf narrated to us, Ja'far ibn Sulayman narrated to us, Harb ibn Shaddad narrated to us, from Qatadah, from Sa'id ibn al-Musayyib, from Sa'd, who said: When the Messenger of Allah (may Allah bless him and grant him peace) went on the expedition of Tabuk, he left Ali behind in Medina. The people said, "He is bored of him and dislikes his company." This reached Ali, so he went out until he caught up with the Prophet (may Allah bless him and grant him peace). He said, "O Messenger of Allah, you left me behind in Medina with the women, the children, and the offspring, until the people said, 'He is bored of him and dislikes his company.'" He said, "O Ali, I only left you behind in charge of my family. Are you not pleased to be to me in the position of Aaron to Moses, except that there is no prophet after me?"