Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When you hear the iqamah, walk calmly; whatever of the prayer you catch, pray it, and whatever you miss, complete it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5145
Abd al-Rahman bin Abi Layla narrates from Mu'adh (may Allah be pleased with him) that the Companions (may Allah be pleased with them) would come to the prayer when the Prophet (peace and blessings be upon him) had already prayed part of the prayer, and they would ask by pointing with one or two fingers towards those praying. Mu'adh (may Allah be pleased with him) came when the Prophet (peace and blessings be upon him) had already prayed part of the prayer, and he too joined the prayer. He says: In whatever state I found the Prophet (peace and blessings be upon him), I joined in that same state. Then I completed the prayer. Then one day he came when part of the prayer had passed, and he joined the prayer. When the Prophet (peace and blessings be upon him) completed the prayer, Mu'adh (may Allah be pleased with him) stood up and was completing the prayer. He (peace and blessings be upon him) said: "Mu'adh has established a way for you; you should do likewise."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5146
Ibn Abi Layla (may Allah have mercy on him) says: Our companions narrated to us that when a man came to pray, he would be told how much of the prayer had passed, and they would be with the Prophet (peace and blessings be upon him) standing, bowing, sitting and praying. Sayyiduna Mu'adh (may Allah be pleased with him) came, and they pointed it out to him. Shu'bah says: I heard this from Husayn, from Ibn Abi Layla, that Sayyiduna Mu'adh (may Allah be pleased with him) said: In whatever state I see the Prophet (peace and blessings be upon him), I will join the prayer in that same state. He (peace and blessings be upon him) said: "Mu'adh (may Allah be pleased with him) has established a way for you; you should do likewise."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5147
Ibn Abi Layla (may Allah have mercy on him) says: until Sayyiduna Mu'adh (may Allah be pleased with him) came. Shu'bah (may Allah have mercy on him) says: I heard from Husayn (may Allah have mercy on him) that Sayyiduna Mu'adh (may Allah be pleased with him) says: "In whatever state I see him (peace and blessings be upon him) — you too do likewise."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5148
Sayyidah Aishah (may Allah be pleased with her) says: When the Messenger of Allah (peace and blessings be upon him) fell ill with the illness in which he (peace and blessings be upon him) passed away, Sayyiduna Bilal (may Allah be pleased with him) came and informed him (peace and blessings be upon him) of the prayer. He (peace and blessings be upon him) said: "Tell Abu Bakr to lead the people in prayer." I said: Sayyiduna Abu Bakr (may Allah be pleased with him) is a tender-hearted man; if he stands in your (peace and blessings be upon him) place, he will weep and will not be able to recite. He (peace and blessings be upon him) said: "Tell Abu Bakr." The third or fourth time he said: "You are like the women of Yusuf. Tell Abu Bakr to lead the people in prayer." Sayyiduna Abu Bakr (may Allah be pleased with him) was leading the people in prayer when the Messenger of Allah (peace and blessings be upon him) came out supported between two men; it is as if I can see him, with his (peace and blessings be upon him) feet drawing lines on the ground. When Sayyiduna Abu Bakr (may Allah be pleased with him) saw him, he began to move back; he (peace and blessings be upon him) signalled to him to carry on leading the prayer. Sayyiduna Abu Bakr (may Allah be pleased with him) remained standing, and the Prophet (peace and blessings be upon him) sat down beside Sayyiduna Abu Bakr (may Allah be pleased with him). He (peace and blessings be upon him) was leading the prayer, and Sayyiduna Abu Bakr (may Allah be pleased with him) was conveying his (peace and blessings be upon him) voice to the people.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5149