Mishkat al-Masabih 4 Prayer كتاب الصلاة 224

وَعَنْهُ أَنَّهُ رَأَى النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُصَلِّي فَإِذَا كَانَ فِي وِتْرٍ مِنْ صَلَاتِهِ لَمْ يَنْهَضْ حَتَّى يَسْتَوِيَ قَاعِدًا. رَوَاهُ البُخَارِيّ

He said that he saw the Prophet praying, and when he had prayed an odd number of rak’as he did not stand up till after he had adopted a sitting position. Bukhari transmitted it.