Does a Muslim forfeit the reward of the afterlife for good deeds if he intends thereby to gain worldly benefit, such as one who gives charity with the intention of healing a sick person, or fasts with the intention of immunity from food?

He who performs a deed purely for the sake of Allah receives a more complete reward. As for one who performs a deed for Allah while intending some worldly benefit associated with the act of worship, such as combining Hajj with trade, his action is valid and he will be rewarded for it, even though the former is more perfect.