Musnad Ahmad 25:240

Waki’ narrated to us, Ibn Dharr narrated to us, from his father, from Sa’id ibn Jubayr, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to Gabriel (peace be upon him): "Why do you not visit us more often than you visit us?" Then it was revealed: "And we do not descend except by the command of your Lord; to Him belongs what is before us and what is behind us" [Maryam: 64], until the end of the verse.