Hadith 2
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (peace and blessings be upon him) said: “The imam has only been appointed to be followed, so do not differ from him. When he says the takbir, say the takbir; when he bows, bow; when he says, Samiʿa -llāhu liman ḥamidah (Allah hears those who praise Him), say, Rabbana laka-l-ḥamd (Our Lord, to You belongs all praise); when he prostrates, prostrate; and when he prays sitting, then all of you pray sitting.”

Hadith 3
ʿĀʾishah (may Allah be pleased with her) said: “The Messenger of Allah (peace and blessings be upon him) prayed in his house while he was unwell; he prayed sitting, and a group behind him prayed standing. He signalled to them, ‘Sit down.’ When he finished, he said, ‘The imam has only been appointed to be followed. When he bows, bow; when he rises, rise; when he says, Samiʿa -llāhu liman ḥamidah, say, Rabbana wa laka-l-ḥamd; and when he prays sitting, then all of you pray sitting.’”

Unfamiliar expressions

1. The prefixed fa in fa-kabbirū, fa-rkaʿū, etc. denotes both order and immediacy: the act is done after the imam and straightaway, neither simultaneously nor after a delay.
2. Juʿila (“has been appointed”) is one of the “verbs of transformation”; it takes two objects, the first appearing here as the passive subject, the second—“imāman” (an imam)—being understood but omitted.
3. Ajmaʿūn (“all together”) is an emphatic particle reinforcing the plural pronoun.
4. Shāk (“ailing”) is an active participle derived from shakwā, meaning illness.

Overall meaning
These two hadiths explain how the congregant should follow the imam. The Prophet (peace and blessings be upon him) makes clear that the very purpose of appointing an imam is that he be emulated; therefore, the worshipper must not depart from him in any motion of the prayer. One watches the imam’s movements in orderly succession: when he pronounces the opening takbir, you pronounce it; when he bows, you bow after him; when he reminds you that Allah hears those who praise Him by saying “Samiʿa -llāhu liman ḥamidah,” you respond with “Rabbana laka-l-ḥamd.” When he prostrates, you prostrate, and if he prays sitting because he cannot stand, then, to realise complete conformity, you too should pray sitting even though you are able to stand.