Musnad Ahmad 937:180

'Abd al-Razzaq narrated to us, Sufyan informed us, from al-A'mash, from 'Amr ibn Murrah, from Abu al-Bakhtari, from Abu Dharr, who said: It was said to the Prophet, peace and blessings of Allah be upon him: "The wealthy have taken away the reward." The Prophet, peace and blessings of Allah be upon him, said: "Indeed, within you there is much charity." He then mentioned the virtue of your hearing and the virtue of your sight. He said: "And in your sexual intercourse with your spouse there is charity." Abu Dharr said: "Would one of us be rewarded for his desire?" He said: "Do you see, if you were to place it in that which is unlawful, would you have a sin upon you?" He said: "Yes." He said: "So do you count the evil, yet you do not count the good?"