Yahya related to me from Malik from Ibn Shihab from Urwa ibn az- Zubayr from A'isha, the wife of the Prophet ﷺ that the Messenger of Allah ﷺ prayed in the mosque one night and people prayed behind him. Then he prayed the next night and there were more people. Then they gathered on the third or fourth night and the Messenger of Allah ﷺ did not come out to them. In the morning, he said, "I saw what you were doing and the only thing that prevented me from coming out to you was that I feared that it would become obligatory (fard) for you." This happened in Ramadan.  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّ رَسُولَ اللَّهِ ﷺ صَلَّى فِي الْمَسْجِدِ ذَاتَ لَيْلَةٍ فَصَلَّى بِصَلاَتِهِ نَاسٌ ثُمَّ صَلَّى اللَّيْلَةَ الْقَابِلَةَ فَكَثُرَ النَّاسُ ثُمَّ اجْتَمَعُوا مِنَ اللَّيْلَةِ الثَّالِثَةِ أَوِ الرَّابِعَةِ فَلَمْ يَخْرُجْ إِلَيْهِمْ رَسُولُ اللَّهِ ﷺ فَلَمَّا أَصْبَحَ قَالَ قَدْ رَأَيْتُ الَّذِي صَنَعْتُمْ وَلَمْ يَمْنَعْنِي مِنَ الْخُرُوجِ إِلَيْكُمْ إِلاَّ أَنِّي خَشِيتُ أَنْ تُفْرَضَ عَلَيْكُمْ وَذَلِكَ فِي رَمَضَانَ  

Yahya related to me from Malik from Ibn Shihab from Abu Salama ibn Abd ar-Rahman ibn Awf from Abu Hurayra that the Messenger of Allah ﷺ used to exhort people to watch the night in prayer in Ramadan but never ordered it definitely. He used to say, "Whoever watches the night in prayer in Ramadan with trust and expectancy, will be forgiven all his previous wrong actions." Ibn Shihab said, "The Messenger of Allah ﷺ died while that was still the custom, and it continued to be the custom in the caliphate of Abu Bakr and at the beginning of the caliphate of Umar ibn al-Khattab."  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يُرَغِّبُ فِي قِيَامِ رَمَضَانَ مِنْ غَيْرِ أَنْ يَأْمُرَ بِعَزِيمَةٍ فَيَقُولُ مَنْ قَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ قَالَ ابْنُ شِهَابٍ فَتُوُفِّيَ رَسُولُ اللَّهِ ﷺ وَالأَمْرُ عَلَى ذَلِكَ ثُمَّ كَانَ الأَمْرُ عَلَى ذَلِكَ فِي خِلاَفَةِ أَبِي بَكْرٍ وَصَدْرًا مِنْ خِلاَفَةِ عُمَرَ بْنِ الْخَطَّابِ