Amatul Rahmân Omer:
Call them (- the adopted ones) after (the names of) their (real) fathers. This is more just and equitable in the sight of Allâh. But if you do not know (the names of) their fathers then (they are) your brothers-in-faith and your friends or wards. And no blame shall lie on you with regard to any mistake you may have unintentionally made (before) in such a case. But (you are accountable for) that which you wilfully and premeditatingly do. And Allâh is Great Protector, Ever Merciful.