Musnad Ahmad 2:124

Abu Abd al-Rahman narrated to us, Haywah narrated to us, Bakr ibn Amr informed me that he heard Abdullah ibn Hubayrah saying: that he heard Abu Tamim al-Jayshani saying: He heard Umar ibn al-Khattab saying: that he heard the Prophet of Allah, peace and blessings of Allah be upon him, saying: "If you were to rely upon Allah with the true reliance due to Him, He would provide for you just as He provides for the birds; they go out hungry in the morning and return with full bellies in the evening."