Musnad Ahmad 30:1708

'Arim narrated to us, he said: 'Abdullah ibn al-Mubarak narrated to us, he said: Muhammad ibn 'Ajlan narrated to me, from Rabi'ah, from al-A'raj, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him—he said: "And I heard it from Rabi'ah and did not deny it"—he said: "The strong believer is better, or more excellent, and more beloved to Allah than the weak believer, and in each there is good. Be eager for what benefits you and do not be incapable. If a matter overcomes you, then say: 'Allah has decreed, and what He willed, He did.' And beware of 'if only' (law), for 'if only' opens [the way] for the devil."