praise be to Allah, the Lord of the Worlds.
When an Imam leads people in prayer, he should be brief for here are among them the weak and the ill. However, being brief does not mean leaving out a pillar or an essential part of the prayer, because Anas reported: "I never prayed behind an Imam who was briefer and more perfect in prayer than the Messenger of Allah (PBUH)." {Related by Muslim}.
Prolonging and shortening prayer is a relative matter, which varies according to time and place. Therefore, the Imam should pay attention to the weak people praying behind him, such as the weak and ill. Jurists have stated the standard governing the difference between the two: the Imam should give enough time for saying three Tasbihat of Ruku` (Bowing down) and Sujud (Prostration), recite short and medium-length Surahs and deliver the Adhkar of standing and sitting between the two Sujuds for the latter are short.
Ibn Hajar Al-Haitami (May Allah have mercy on him) said: "It is recommended that an Imam be brief when leading people in prayer along with delivering the obligatory as well as the desirable acts of the prayer. This is based on the Hadith in which the Prophet said: "He who acts as Imam of the people, he must be brief, for among them are the aged, among them are the sick, among them are the weak, and among them are the people who have business to attend. But when any of you prays alone, he may pray as he likes." {Related by Bukhari & Muslim}.
In conclusion, the standard is reciting short and medium-length Surahs, delivering the Tasbih of Sujud and Ruku` and the Adhkar of standing and sitting between the two Sujuds. And Allah Knows Best.
