Bayhaqi 5307 — Leading the prayer by order of the ruler

Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) says: There was fighting among Banu Amr bin Awf. The news reached the Prophet (peace and blessings be upon him), so he (peace and blessings be upon him) came to them after Zuhr to make peace between them. He (peace and blessings be upon him) said to Sayyiduna Bilal (may Allah be pleased with him): "If the time of Asr comes and I have not come back to you, tell Abu Bakr (may Allah be pleased with him) to lead the prayer." When the time of Asr came, Sayyiduna Bilal (may Allah be pleased with him) called the adhan, then the iqamah, then told Sayyiduna Abu Bakr (may Allah be pleased with him), and he went forward. At the end of this hadith it says: "When something happens in the prayer, the men are to say 'Subhan Allah' (Allah is free of all imperfection), and the women are to clap."
His words to Bilal in this hadith are an addition that Hammad bin Zayd preserved, and an addition in such a case is accepted. And Allah knows best.