Aayesha Radiyallahu 'Anha reports:
"Rasulullah Sallallahu 'Alayhi Wasallam performed most of his (nafl) salaah in a sitting posture before he passed away". (JA)
English reference (JA): Book 39, Hadith 266 (JA)
Arabic reference (JA): Book 40, Hadith 282 (JA)