What is the ruling on intoning the Qur’an (tajwid) in prayer in the following cases: an imam leading people in a loud prayer, a worshiper praying silently behind the imam, and an individual praying an obligatory or supererogatory prayer?

Allah Almighty commanded the recitation of the Qur’an in tartil (slow, melodious recitation), and scholars did not differentiate in this command between reciting during prayer and outside of it, or between whispering and vocalizing, or between the recitation of the Imam, the congregant, and the individual. Tartil is required from every able reciter, as it increases humility, understanding, and tranquility. The Salaf (pious predecessors) forbade recitation that was not tajwid-compliant (i.e., not well-recited). The Prophet, peace and blessings be upon him, used to recite the Qur’an in tartil, elongating its letters and beautifying them.