[Kitdowstyhodo]

Wa 'alaikum assalam wa rahmatullah,

A teacher said to supplicate using:

"Rabbi hab lee min ladunka dhurriyatan tayyibah. Innaka samee'u -al du'aa`"

رَبِّ هَبۡ لِى مِن لَّدُنكَ ذُرِّيَّةً۬ طَيِّبَةً*ۖ إِنَّكَ سَمِيعُ ٱلدُّعَآءِ

O my Lord grant me from your own a good offspring. Indeed you are the hearer of supplications.

I think you should recite it either 3 or 7 times after each prayer (can't remember exactly)