Abu Sa'id (al Khudri) reported Allah's Apostle ﷺ as saying: Observe Witr prayer before it is morning. Abu Sa'id reported that they (the Prophet's Companions) asked the Apostle of Allah ﷺ about Witr (prayer). (In reply to their inquiry) he said: Observe Witr prayer before it is morning.

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ الأَعْلَى بْنُ عَبْدِ الأَعْلَى، عَنْ مَعْمَرٍ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي سَعِيدٍ، أَنَّ النَّبِيَّ ﷺ قَالَ
" أَوْتِرُوا قَبْلَ أَنْ تُصْبِحُوا " .