Is it permissible to offer money to someone to perform a good deed, such as giving 500 dirhams to an uncle to grow his beard?

It is permissible to offer and give money to someone who adheres to the rulings of Islamic law, such as growing a beard, as an encouragement for him to obey. As for the recipient, if he grows his beard for the sake of the reward, he will not receive any recompense unless the reward was a motivator for him to implement what Allah has commanded, or his intention changed after he committed to it. A sound intention is a prerequisite for recompense, and there is no harm in starting for the sake of the reward.