A couple of traditional sayings that convey the same idea:
Is binn béal ina thost. (A mouth when silent sounds sweet.)
Is minic a bhris béal duine a shrón. (A man's mouth has often broken his nose.)
Tá seanfhocail eile mar sin ann, nach bhfuil?
Dennis King - Stair an Fhocail: suigh http://www.eskimo.com/~donncha/stair3.html