From the Islamic standpoint, Sunnah refers to anything narrated or related about the Prophet Muhammad (peace be upon him), authentically traced to him regarding his speech, actions, traits, and silent approvals, before and after the revelation.
Each narration is composed of two parts: the isnad and the matn. The isnad refers to a chain of people who narrated a paricular narration. The matn is the actual text of the narration. The isnad must comprise upright and sincere individuals whose integrity is unquestionable.
The speech of Prophet Muhammad (peace be upon him) refers to his sayings. For example, he said:
"Actions are judged by their intentions; everyone will be rewarded according to his/her intention. So whoever migrates for the sake of Allah and His Prophet then his migration will be noted as a migration for the sake of Allah and His Prophet. Conversely, one who migrates only to obtain something worldly or to marry a woman, then his migration will be worth what he had intended." [Bukhari]
The Prophet (peace be upon him) also said:
"Whoever believes in Allah and the Last Day, should say something good or keep quiet."