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
tirmidhi:3371 – ʿAlī b. Ḥujr > al-Walīd b. Muslim > Ibn Lahīʿah > ʿUbaydullāh b. Abū Jaʿfar > Abān b. Ṣāliḥ > Anas b. Mālik

the Prophet said: “The supplication is the essence of worship.”  

الترمذي:٣٣٧١ – حَدَّثَنَا عَلِيُّ بْنُ حُجْرٍ أَخْبَرَنَا الْوَلِيدُ بْنُ مُسْلِمٍ عَنِ ابْنِ لَهِيعَةَ عَنْ عُبَيْدِ اللَّهِ بْنِ أَبِي جَعْفَرٍ عَنْ أَبَانَ بْنِ صَالِحٍ عَنْ أَنَسِ بْنِ مَالِكٍ

عَنِ النَّبِيِّ ﷺ قَالَ الدُّعَاءُ مُخُّ الْعِبَادَةِ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ غَرِيبٌ مِنْ هَذَا الْوَجْهِ لاَ نَعْرِفُهُ إِلاَّ مِنْ حَدِيثِ ابْنِ لَهِيعَةَ

See similar narrations below:

Collected by Suyūṭī