Yahya related to me from Malik from Ibn Shihab that Abdullah ibn Amr ibn al As said, "When we arrived at Madina we were struck down by a severe epidemic which debilitated us greatly. The Messenger of Allah ﷺ came out to the people while they were praying nawafil prayers sitting down. The Messenger of Allah ﷺ said, 'The prayer of the one sitting is equal to only half the prayer of the one standing.' "
أَنَّهُ قَالَ لَمَّا قَدِمْنَا الْمَدِينَةَ نَالَنَا وَبَاءٌ مِنْ وَعْكِهَا شَدِيدٌ فَخَرَجَ رَسُولُ اللَّهِ ﷺ عَلَى النَّاسِ وَهُمْ يُصَلُّونَ فِي سُبْحَتِهِمْ قُعُودًا فَقَالَ رَسُولُ اللَّهِ ﷺ صَلاَةُ الْقَاعِدِ مِثْلُ نِصْفِ صَلاَةِ الْقَائِمِ