Jami` at-Tirmidhi 3478

Asma bint Yazid narrated that the Prophet (ﷺ) said:“Allah's greatest name is in these two Ayah: ‘And your deity is One deity, there is none who has the right to be worshipped but He, Ar-Raḥmān, Ar-Raḥīm.’ And the Opening of Al-`Imrān: ‘Alif. Lām. Mīm. Allah, None has the right to be worshipped but He, the Ever living, the Sustainer.’”