Abu Dawud said: The tradition narrated by 'Abbad is more perfect (than the version narrated by Musaddad). Musaddad did not mention in his version "the command (of good) and the prohibition (of evil)". Instead, he added in his version saying: "Such and such." Ibn Ma'na added in his version: "They (the people) said: Messenger of Allah, how is that one of us fulfills his desire and still there are alms for him (i.e. is rewarded)? He replied: What do you think if you had unlawful sexual intercourse, would he not have been a sinner ?
In-book : Book 5, Hadith 36
English translation : Book 5, Hadith 1280