What are the recommended recitation speed and length for the Imam and the individual worshipper?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
It is recommended for the Imam to recite, glorify, and perform the Tashahhud slowly enough so that those behind him who have difficulty speaking can complete them, and so that they can complete their bowing and prostration adequately. For the individual worshipper, they have the right to prolong these acts, unless the prolongation leads to a state where they might forget or make an error in the prayer, in which case prolongation beyond that point becomes disliked.
Supporting text
The Imam should not prolong the prayer excessively, as this causes hardship for the congregation, based on the command: 'Whoever leads the people in prayer, let him make it light.' If the Imam shortens the recitation to accommodate those behind him, it is disliked but valid. If an unforeseen event requires some in the congregation to leave, the Imam should shorten the prayer, as the Prophet (PBUH) used to lighten the prayer upon hearing a child crying, out of dislike for causing hardship to the mother.