Musnad Ahmad 25:205

Ya'la narrated to us, Umar 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: "What prevents you from visiting us more than you visit us?" He said: Then it was revealed: {And we do not descend except by the command of your Lord} [Maryam: 64] until the end of the verse.