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:39:2 –

Indeed, We have sent down to you the Book, ˹O Muhammad˺, in truth. So worship Allah, ˹being˺ sincere to Him in religion.  

Indeed We have revealed to you, O Muhammad (s), the Book with the truth (bi’l-haqqi is semantically connected to anzalnā, ‘We have revealed’); so worship God, devoting your religion purely to Him, ˹pure˺ of any idolatry, in other words, affirming His Oneness.
القرآن:٣٩:٢ –

إِنَّا أَنْزَلْنَا إِلَيْكَ الْكِتَابَ بِالْحَقِّ فَاعْبُدِ اللَّهَ مُخْلِصًا لَهُ الدِّينَ  

{إنا أنزلنا إليك} يا محمد {الكتاب بالحق} متعلق بأنزل {فاعبد الله مخلصا له الدين} من الشرك: أي موحدا له.

See similar narrations below:

Collected by Qurʾān
quran:39:11 –

Say, ˹O Muhammad˺, "Indeed, I have been commanded to worship Allah, ˹being˺ sincere to Him in religion.  

Say: ‘Indeed I have been commanded to worship God devoting ˹my˺ religion purely to Him, ˹pure˺ of any idolatry,
القرآن:٣٩:١١ –

قُلْ إِنِّي أُمِرْتُ أَنْ أَعْبُدَ اللَّهَ مُخْلِصًا لَهُ الدِّينَ  

{قل إني أمرت أن أعبد الله مخلصا له الدين} من الشرك.