Superiority of performance of four Rak'at
at the forenoon
78) Narrated Na'im bin Hammar Al-Ghatfani that he heard Allah's Messenger saying: Allah said: 0 son of Adam! Don't feel short of performing four Rak'at (prayer) at the forenoon. (If you do so) I will safeguard you (against the Satan) for the rest of the day.
(This Haditb is sound and reported by Ahmad in his Musnad and Abu Da'ud and Ibn Hibban).
Voluntary prayers are mostly preferable at the night, but the Prophet used to perform two (Raka ') by day in the forenoon. This is known to be the Duha prayer. It can also be four Raka' or more; six or eight if you like.