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:38:17 –

Be patient over what they say and remember Our servant, David, the possessor of strength; indeed, he was one who repeatedly turned back ˹to Allah˺.  

God, exalted be He, says: Bear patiently what they say and remember Our servant David, the one of fortitude, that is to say, ˹the one˺ of fortitude in worship: he used to fast every other day and keep vigil for half the night, sleep for a third and then keep vigil for the ˹last˺ sixth. Indeed he was a penitent ˹soul˺, always returning to what pleases God.
القرآن:٣٨:١٧ –

اصْبِرْ عَلَىٰ مَا يَقُولُونَ وَاذْكُرْ عَبْدَنَا دَاوُودَ ذَا الْأَيْدِ ۖ إِنَّهُ أَوَّابٌ  

قال تعالى: {اصبر على ما يقولون واذكر عبدنا داود ذا الأيد} أي القوة في العبادة كان يصوم يوما ويفطر يوما ويقوم نصف الليل وينام ثلثه ويقوم سدسه {إنه أوَّاب} رجّاع إلى مرضاة الله.