Some people from amongst the Companions of the Messenger of Allah (ﷺ) said to the Prophet (ﷺ), "O Messenger of Allah, the affluent have made off with the rewards; they pray as we pray, they fast as we fast, and they give [much] in charity by virtue of their wealth." He (ﷺ) said, "Has not Allah made things for you to give in charity? Truly every tasbeehah [saying: 'subhan-Allah'] is a charity, and every takbeerah [saying: 'Allahu akbar'] is a charity, and every tahmeedah [saying: 'al-hamdu lillah'] is a charity, and every tahleelah [saying: 'laa ilaha illAllah'] is a charity. And commanding the good is a charity, and forbidding an evil is a charity, and in the bud`i [sexual act] of each one of you there is a charity." They said, "O Messenger of Allah, when one of us fulfils his carnal desire will he have some reward for that?" He (ﷺ) said, "Do you not see that if he were to act upon it [his desire] in an unlawful manner then he would be deserving of punishment? Likewise, if he were to act upon it in a lawful manner then he will be deserving of a reward."

[Muslim]