Ibrahim bin Sa'd bin Ibrahim إبراهيم بن سعد بن إبراهيم · The Book of Marriage

"The Messenger of Allah used to teach his Companions to perform Istikharah in all matters, just as he used to teach them Surahs from the Qur'an. He said: 'If any one of you is deliberating about a decision he has to make, then let him pray two Rak'ahs of non-obligatory prayer, then say: Allahumma inni astakhiruka bi 'ilmika wa astaqdiruka bi qudratika wa as'aluka min fadlika, fa innaka taqdiru wa la aqdir, wa ta'lamu wa la a'lam, wa anta 'allam…

"The Messenger of Allah married me when I was seven years old, and he consummated the marriage with me when I was nine."