Musnad Abu Ya'la al-Mawsili 2:108

Abu Khaythama narrated to us, Abdullah bin Yazid narrated to us, from Haywah bin Shurayh, from Bakr bin Amr, from Abdullah bin Hubayrah, from Abu Tamim al-Jayshani, from Umar bin al-Khattab, who said: 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; they go out in the morning hungry and return in the evening with full bellies."