Sahih Muslim | Book 33 | Hadith Number 6441

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: A strong believer is better and is more lovable to Allah than a weak believer, and there is good in everyone, (but) cherish that which gives you benefit (in the Hereafter) and seek help from Allah and do not lose heart, and if anything (in the form of trouble) comes to you, don't say: If I had not done that, it would not have happened so and so, but say: Allah did that what He had ordained to do and your "if" opens the (gate) for the Satan.