Facebook Messenger displays a notification for each new message, and when participating in group chats with a lot of active members, you can expect to receive a lot of them. The Mute feature allows you put a stop to the flood of notifications on Facebook Messenger.
How To Mute a Conversation in Messenger
Open the Facebook Messenger app, hold your finger down on the desired conversation and select Mute notifications:
How To Mute a Group Chat in Messenger
Go to the Group tab and tap on the More menu (3 vertical dots) displayed at the top right corner of the desired group. Select Mute Notifications:
You can choose to mute notifications for the selected conversation or group for a specific time period (15 minutes, 1 hour, 8 hours...) or until you manually unmute it. Furthermore, if you have an alarm configured on your smartphone, you can choose to mute notifications until the alarm goes off:
N.B. You can set up your alarm in Settings > Clock > Alarm.