المتين
كلمة (المتين) في اللغة صفة مشبهة باسم الفاعل على وزن (فعيل) وهو...
Two prostrations performed in order to make up for a deficiency in the prayer due to forgetfulness.
"Sujood-us-sahw" (prostration of forgetfulness) consists of two prostrations similar in posture and "dhikr" (expressions of remembrance of Allah) to the prostration done in regular prayer. The imam (and those praying behind him) as well as the one praying by himself have to perform them in case one of the three reasons of forgetfulness occurs, they are: 1. Addition. 2. Reduction. 3. Doubt. In case of addition, one has to prostrate before the "tasleem" (ending the prayer with the "salaam" greeting); and in case of reduction, one has to prostrate after the "tasleem".
To place one’s forehead and nose on the floor twice at the end of prayer. These two prostrations are done to redress an unintended error of commission or omission during prayer.