It is reported that Imâm Layth b. Sa’d – Allâh have mercy on him – said, “Even if I saw a heretic (follower of bid’ah) walk on water, I would not accept him.” This was reported to Imâm Al-Shâfi’î – Allâh have mercy on him, to which he replied, “He didn’t go far enough. Rather, if I saw one walk in the air, I would not accept him.”

Al-Lâlakâ`î, Sharh Usûl ‘I’tiqâd Ahl Al-Sunnah Vol.1 p228; Ibn Battah, Al-Ibânah Al-Kubrâ Vol2. P175; Ibn Al-Jawzî, Talbîs Iblîs p14 – with slightly variant wordings.