Bismillaah-ir-Rahmaan-ir-Raheem
Allaah the Mighty is Sublime and Infinite in His Wisdom. He bestows offspring to His slaves as He wishes.
Our brother, Misbaah Olagunju, has made a little compilation you can read at a-go Inshaa Allaah, all about the lessons and wisdom in this phenomenon.
Click here to download.
