Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.032.

Section : Salatul Istikharah.It is a sunnah that, if one must choose between permissible alternatives, one may pray two non-obligatory rak'at, even if they are of the regular sunnah prayers or a prayer for entering the mosque, and so on, during any time of the day or night, and to recite therein whatever one wishes … Continue reading Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.032.