BT Qid 36a(40) :כי ל׳ע!א להו הימנותא איקרו בנים , כי קא פלחי ע׳ז לא‏ : when they do (not!) have faith they are called "sons" but when they worship idolatry they are not
See the entire entry for haymānū, haymānūṯā n.f. faithfulness; religion