Sunan an Nasai
The Book of The At-Tatbiq (Clasping One's Hands Together)
Hadith #124
12.124
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ أَنْبَأَنَا هُشَيْمٌ، عَنْ خَالِدٍ، عَنْ أَبِي قِلاَبَةَ، عَنْ مَالِكِ بْنِ الْحُوَيْرِثِ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُصَلِّي فَإِذَا كَانَ فِي وَتْرٍ مِنْ صَلاَتِهِ لَمْ يَنْهَضْ حَتَّى يَسْتَوِيَ جَالِسًا .
It was narrated that Malik bin Al-Huwairith said:"I saw the Messenger of Allah (ﷺ) pray, and when he was in an odd-numbered rak'ah, he did not get up until he had settled in a sitting position