Musnad Ahmad 30:1903

'Affan narrated to us, Abu 'Awanah narrated to us, 'Umar ibn Abi Salamah narrated to us, from his father, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "When one of you wishes, let him look at what he is wishing for, for he does not know what will be written for him from his wish."