Hadithcore
Mishkat al-Masabih, 1198

‘A’isha said, “When God’s Messenger grew old and was ill, he mostly prayed sitting.” (Bukhari and Muslim.)

وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: لَمَّا بَدَّنَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَثَقُلَ كَانَ أَكْثَرُ صَلَاتِهِ جَالِسًا

References1 variant
In-Book Reference
Book 4, Hadith 614