If an imam accidentally recites quietly in the first two rakahs of Maghrib instead of audibly, the required mode of recitation has been omitted. Sujud al-sahw becomes due, and followers join the imam in those prostrations.
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Application: imam recites Maghrib quietly
Prostrations of Forgetfulness: Causes, Method, Missed Sittings and Doubts
If an imam accidentally recites quietly in the first two rakahs of Maghrib instead of audibly, the required mode of recitation has been omitted. Sujud al-sahw becomes due, and followers join the imam in those prostrations.