Fiqh-us-Sunnah Volume 002, Supererogatory Prayer, Fiqh 2.033A.

Section : Salatul Hajah, the prayer for need.

Ahmad has on sound authority reported from Abu Darda that the Prophet Sallallahu Alehi wasallam said: "He who makes wudu, and does it properly, then prays two rak'at, Allah will grant him whatever he may pray for, sooner or later."