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
ahmad-zuhd:1214 – ʿAbdullāh > Abū Bakr > Abū al-Aḥwaṣ > Manṣūr > Mujāhid And Tabattal Ilayh Tabtīl al-Mzml 8

[Machine] "And turn towards Him a sincere turning." [Surah al-Muzzammil 8] He said, "Purify the intention with utmost sincerity."  

الزهد لأحمد:١٢١٤ – حَدَّثَنَا عَبْدُ اللَّهِ حَدَّثَنَا أَبُو بَكْرٍ حَدَّثَنَا أَبُو الْأَحْوَصِ عَنْ مَنْصُورٍ عَنْ مُجَاهِدٍ

{وَتَبَتَّلْ إِلَيْهِ تَبْتِيلًا} [المزمل 8] قَالَ أَخْلِصِ النِّيَّةَ إِخْلَاصًا  

See similar narrations below:

Collected by Aḥmad's Zuhd
ahmad-zuhd:1519 – ʿAbdullāh > Naṣr b. ʿAlī > Muslim b. Qutaybah > Sahl al-Sarrāj > al-Ḥasan And Tabattal Ilayh Tabtīl al-Mzml 8

[Machine] "Purify your intentions for Him with utmost sincerity."  

الزهد لأحمد:١٥١٩ – حَدَّثَنَا عَبْدُ اللَّهِ حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ أَخْبَرَنِي مُسْلِمُ بْنُ قُتَيْبَةَ حَدَّثَنَا سَهْلٌ السَّرَّاجُ عَنِ الْحَسَنِ {وَتَبَتَّلْ إِلَيْهِ تَبْتِيلًا} [المزمل 8] قَالَ

«أَخْلِصْ إِلَيْهِ إِخْلَاصًا»