Sayyiduna Abu al-Darda' (may Allah be pleased with him) said: My dear friend (that is, the Prophet (peace and blessings be upon him)) advised me to do three things: to fast three days every month, to pray witr before sleeping, and (to pray the sunnah of) the two rak'ahs of Fajr.
(Allamah al-Haythami said:) I say: Abu Dawud recorded this narration, but he did not mention the two rak'ahs of Fajr.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are the narrators of the Sahih.