"A believer who is strong (and healthy) is better and dearer to Allah than the weak believer, but there is goodness in both of them. Be keen on what benefits you and seek help from Allah, and do not give up. If anything afflicts you do not say, "If I had done such and such things, such and such would have happened.' But say, "Allah decrees and what He wills He does,' for (the utterance) "If I had' provides an opening for the deeds of the devil."

Related by Muslim.