Sunan Abi Dawud Book 5, Hadith 36
The Prophet (ﷺ) as saying: In the morning alms are due for every bone in man's body. His salutation to everyone he meets is alms, his enjoining good is alms, his forbidding what is evil is alms, the removal of harmful thing from the way is alms, to have sexual intercourse with one's wife if alms, and two rak'ahs which one prays in the Duha serve instead of that.
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 ?
Ibn 'Umar was asked about praying two rak'ahs before the Maghrib prayer. He replied: I did not see anyone praying them during the time of the Messenger of Allah (ﷺ). He (Ibn Umar) permitted to pray two rak'ahs after the Asr prayer.
Abu Dawud said: I heard Yahya b. Ma'in say: The correct name of the narrator Abu Shu'aib is the Shu'aib. Shu'bah made a mistake in narrating his name.
While we were present with Abu Dharr, he said: In the morning, alms are due for him, ever fast is alms, every pilgrimage is alms, every utterance of "Glory to be Allah" is alms, every utterance of "Allah is most great" is alms, every utterance of "Praise be to Allah" is alms. The Messenger of Allah (ﷺ) recounted all such good works. He then said: Two rak'ahs which one prays in the Duha serve instead of that.