SAHIH MUSLIM

Umm Habiba, the wife of the Prophet of Allaah (sallAllaahu alayhi wa sallam), reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: If any Muslim servant (of Allaah) prays for the sake of Allaah twelve rak'ahs (of Sun'an) every day, over and above the obligatory ones, Allaah will build for him a house in Paradise, or a house will be built for him in Paradise; and I have not abandoned to observe the in after (hearing it from the Messenger of Allaah). (So said also 'Amr and Nu'man.)