Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:2:163 –

And your god is one God. There is no deity ˹worthy of worship˺ except Him, the Entirely Merciful, the Especially Merciful.  

When they asked him ˹Muhammad (s)˺ to describe his Lord, the following was revealed: Your God, the One deserving of your worship, is One God, without any equal in either essence or attribute; there is no god except Him, He is the Compassionate, the Merciful.
القرآن:٢:١٦٣ –

وَإِلَٰهُكُمْ إِلَٰهٌ وَاحِدٌ ۖ لَا إِلَٰهَ إِلَّا هُوَ الرَّحْمَٰنُ الرَّحِيمُ  

ونزل لما قالوا صف لنا ربك: {وإلهكم} المستحق للعبادة منكم {إِلهٌ واحد} لا نظير له في ذاته ولا في صفاته {لا إلهَ إلا هو} هو {الرحمن الرحيم} وطلبوا آيه على ذلك فنزل.

See similar narrations below:

Collected by Ibn Mājah
ibnmajah:3855 – Abū Bakr > ʿĪsá b. Yūnus > ʿUbaydullāh b. Abū Ziyād > Shahr b. Ḥawshab > Asmāʾ b. Yazīd

the Messenger of Allah (saas) said: "The Greatest Name of Allah is in these two Verses: And your Ilah (God) is One Ilah (God - Allah), La Ilaha Illa Huwa (none has the right to be worshipped but He), the Most Gracious, the Most Merciful.' And at the beginning of Surah Al 'Imran."  

ابن ماجة:٣٨٥٥ – حَدَّثَنَا أَبُو بَكْرٍ حَدَّثَنَا عِيسَى بْنُ يُونُسَ عَنْ عُبَيْدِ اللَّهِ بْنِ أَبِي زِيَادٍ عَنْ شَهْرِ بْنِ حَوْشَبٍ عَنْ أَسْمَاءَ بِنْتِ يَزِيدَ قَالَتْ

قَالَ رَسُولُ اللَّهِ ﷺ اسْمُ اللَّهِ الأَعْظَمُ فِي هَاتَيْنِ الآيَتَيْنِ {وَإِلَهُكُمْ إِلَهٌ وَاحِدٌ لاَ إِلَهَ إِلاَّ هُوَ الرَّحْمَنُ الرَّحِيمُ} وَفَاتِحَةِ سُورَةِ آلِ عِمْرَانَ