The narrator's father said: I asked Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) about praying behind a Qadari, and he said: Do not pray behind him. As for me, had I prayed behind him, I would have repeated my prayer.
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18344