Chapter on the Rulings of Congregational Prayer (the Minimum Number for Congregational Prayer, the Description of the Imam, Who Is to Be Followed and Who Is Not to Be Followed, Recitation Behind Both of Them, the Rulings of Those Led in Prayer, and Other Such Rulings Related to It)

Tahdhīb al-Aḥkām|Volume 3|Book 1|Chapter 3

Tahdhīb al-Aḥkām

Volume 3, Book 1, Chapter 3

Chapter on the Rulings of Congregational Prayer (the Minimum Number for Congregational Prayer, the Description of the Imam, Who Is to Be Followed and Who Is Not to Be Followed, Recitation Behind Both of Them, the Rulings of Those Led in Prayer, and Other Such Rulings Related to It)

Commentary #39

والامام إذا صلى بقوم فركع ودخل أقوام فليطل الركوع حتى يلحق الناس بالصلاة ومقدار ذلك أن يكون ضعفي ركوعه

And when the imam (of prayer) is leading a group in prayer and he goes into rukuh while others are entering (the prayer), he should lengthen the rukuh so that the people may catch up with the prayer. The extent of that is that it should be twice the length of his normal ruku.