Sunan an-Nasai Book 21, Hadith 1831

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ أَنَسٍ، قَالَ آخِرُ نَظْرَةٍ نَظَرْتُهَا إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم كَشَفَ السِّتَارَةَ وَالنَّاسُ صُفُوفٌ خَلْفَ أَبِي بَكْرٍ رضى الله عنه فَأَرَادَ أَبُو بَكْرٍ أَنْ يَرْتَدَّ فَأَشَارَ إِلَيْهِمْ أَنِ امْكُثُوا وَأَلْقَى السِّجْفَ وَتُوُفِّيَ مِنْ آخِرِ ذَلِكَ الْيَوْمِ وَذَلِكَ يَوْمُ الاِثْنَيْنِ ‏.‏

It was narrated that Anas said:"The last time I saw the Messenger of Allah, he drew back the curtain when the people were in rows behind Abu Bakr, may Allah be pleased with him. Abu Bakr wanted to step back, but he gestured to them to stay as they were, and let the curtain drop. He died at the end of that day, and that was a Monday