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:19:3 –

When he called to his Lord a private supplication.  

when (idh is semantically connected to rahma, ‘mercy’) he called out to his Lord a call, entailing a supplication, in secret, in the middle of the night, because this ˹time of the night˺ invites a faster response ˹to one’s supplication˺.
القرآن:١٩:٣ –

إِذْ نَادَىٰ رَبَّهُ نِدَاءً خَفِيًّا  

{إذ} متعلق برحمة {نادى ربه نداءً} مشتملاً على دعاء {خفيا} سرا جوف الليل لأنه أسرع للإجابة.