Hadithcore
Mishkat al-Masabih, 2291

Asma’ daughter of Yazid reported the Prophet (ﷺ) as saying, “God’s greatest name is in these two verses, ‘And your God is one God; there is no god but He, the Compassionate, the Merciful’ [Qur'an, ii, 163.], and the beginning of <i>Al 'Imran</i>, ‘A.L.M. God, there is no god but He, the Living, the Eternal’ [Qur'an, iii. 1.]” Tirmidhi, Abu Dawud, Ibn Majah and Darimi transmitted it.

وَعَنْ أَسْمَاءَ بِنْتِ يَزِيدَ رَضِيَ اللَّهُ عَنْهَا أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: " اسْمُ اللَّهِ الْأَعْظَمُ فِي هَاتَيْنِ الْآيَتَيْنِ: (وَإِلَهُكُمْ إِلَهٌ وَاحِدٌ لَا إِلَهَ إِلَّا هُوَ الرَّحْمَنُ الرَّحيمُ) وفاتحة (آل عمرانَ) : (آلم اللَّهُ لَا إِلَهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ) رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَابْنُ مَاجَهْ وَالدَّارِمِيُّ

References1 variant
In-Book Reference
Book 9, Hadith 65