Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

If the bleeding follows the miscarriage – after the embryo has become a fetus –  then it is considered post- natal bleeding and you should abstain from prayer as long as bleeding lasts. If however, the bleeding started before miscarriage happened then you should continue prayer as long as it is not related to your menses.

Majority of scholars are of the view that in the event of miscarriage after the embryo has assumed a human form, the bleeding is considered as due to nifas or bleeding of childbirth. If it happens before, then the bleeding should not be treated as due to childbirth. It falls into the category of chronic bleeding in which case one should offer prayers after washing the private parts and performing fresh ablution before each prayer.

Almighty Allah knows best.