Musnad Ahmad 2:291

Yahya ibn Ishaq narrated to us, Ibn Lahi'ah informed us, Abdullah ibn Hubayrah narrated to us, he said: I heard Abu Tamim al-Jayshani saying: I heard Umar ibn al-Khattab saying: I heard the Messenger 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; do you not see that they go out hungry in the morning and return with full bellies in the evening?"