His saying: "Alif-Lam-Mim." The discussion regarding it has already passed at the beginning of Surat al-Baqarah.
قَوْله: ﴿الم﴾ قَدْ مَضَى (الْقَوْلُ فِيهِ) فِي أول سُورَة الْبَقَرَة