(a) Sayyidah Aishah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) was ill, so he ordered Sayyiduna Abu Bakr (may Allah be pleased with him) to lead the prayer. Then the Messenger of Allah (peace and blessings be upon him) felt some improvement in himself, so he came and sat at the side of Sayyiduna Abu Bakr (may Allah be pleased with him). The Messenger of Allah (peace and blessings be upon him) was leading Sayyiduna Abu Bakr (may Allah be pleased with him) in prayer while sitting, and Sayyiduna Abu Bakr (may Allah be pleased with him) was leading the people in prayer while standing.
(b) He (peace and blessings be upon him) offered the prayer sitting during the days of his illness. In this hadith there is evidence for what we pointed to in this chapter. In Sayyiduna Abu Bakr (may Allah be pleased with him) standing while he (peace and blessings be upon him) led the prayer sitting, there is evidence that the earlier command was abrogated, and that the correct position is that the follower prays standing even if the imam prays sitting because of a valid excuse. And success is from Allah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3658