to perform the recommended acts, such as reciting a surah and uttering the tasbih three times during bowing and prostration.
It is Sunnah for the imam to recite in measured tones, and to pause during the tasbih and the tashahhud long enough for those behind him to complete the prescribed glorifications and the like, and to settle properly into their bowing and prostration.
It is also Sunnah for the imam to lengthen the first rak‘ah, for Abu Qatadah reported, “The Prophet used to prolong the first rak‘ah,” and the report is agreed upon.
Furthermore, if while in bowing the imam senses someone entering the mosque, it is recommended that he extend the bowing so that the newcomer can join and thereby catch the rak‘ah, assisting him in this regard. Ahmad and Abu Dawud relate from Ibn Abi Awfa—concerning the description of the Prophet’s prayer—that he would remain standing in the first rak‘ah of the noon prayer until no footfall could be heard, provided that such waiting does not burden those already praying. If it would burden them, he should not wait, for the right of those present with him outweighs the right of one who has not yet joined.
In short, the imam must take the condition of the congregation into account, see to the completion and sound performance of the prayer, and model himself on the guidance of the Prophet, acting upon his counsels and commands; therein lies benefit for all.
Some imams, however, grow lax regarding the office of leadership and its responsibilities, frequently absenting themselves from the mosque or arriving late, placing the congregation in an awkward position and causing