Devotion to the sunnah (practices of the Prophet) is expressed as al-i‘tisam bi's-sunnah in Islamic literature. The literal meanings of al-i'tisam are as follows; holding, devotion, adhering to, taking refuge in, acquiring power, gaining power, calling for help, self protection, abstention.
The term i'tisam is not frequently used in the Quran. "He who holds fast (devoted) to Allah, he indeed is guided unto a right path." (Al-Imran 3/101) "And hold fast, all of you together, to the rope of Allah, and do not separate." (Al-Imran 3/103). In such verses the initial meaning of the term i'tisam is that of holding. Moreover, in all the verses where the term i'tisam is found it is in connection with Allah.
Within the hadith (saying of the Prophet), the most important use of the term i'tisam with the meaning "holding" is the phrase: "I left you with two things to hold onto; The book of Allah and the sunnah of His Messenger"
The phrase al-i‘tisam bi's-sunnah was first used by Prophet Muhammad (pbuh) not orally, but as a concept and its first usage occurred in the era of the Companions. The term can be found in the hadith books as the heading of a section; this began with al-Bukhari and can be treated as a separate book.
The term i'tisam with the meaning "devotion to the sunnah" implies that life itself should be organized in accordance with the sunnah. With this respect, Islam is practiced at a moderate level. It never possesses an excessive quality in relation to its meaning. The attitudes and deeds of Prophet Muhammad, and as a result his life itself, constitutes evidence of this. Thus, obeying the sunnah is not an act of "imitation", but rather one of "obedience".
The Holy Quran Commands al-I‘tisam
Although there is no direct order about "al-itisam to the sunnah", there are many verses that imply this issue. The following verse generally and briefly explains al-i‘tisam to the sunnah in a manner that covers the sunnah as a whole: "And whatsoever the messenger gives you, take it. And whatsoever He forbids, abstain from it!" (Al-Hashr 59/7). The Companions believed that this verse covered the sunnah as a whole.
The verses which command that the Prophet be believed and obeyed also indicate the necessity of al-i‘tisam in terms of the status of the Prophet and his sunnah.
The verse, "Who obeys the messenger also obeys Allah" (Al-Nisaa 4/80) indicates why obedience to Prophet Muhammad is important and why it is necessary. The verses that order obedience to the Prophet state that obedience to him is also obedience to Allah, as can be seen in the following verse: "Obey Allah and obey His messenger; but if you turn away, then the duty of Our messenger is only to convey the message plainly" (Al-Taghabun 64/12). Here obedience to the Prophet is mentioned along with obedience to Allah. Due to the fact that obedience to Prophet Muhammad and obedience to Allah are stated separately, there is an "obedience" field that has been set aside for the Prophet, and this means that he gave judgments about issues that were not mentioned in the Quran.
The necessity of al-i‘tisam to the sunnah is clearly emphasized in the following verses: "And it becomes not a believing man or a believing woman, when Allah and His messenger have decided an affair for them, that they should after that claim any say in their affair; and whoso is rebellious to Allah and His messenger, he verily goes astray in error manifest" (Al-Ahzab 33/36) and "But nay, by thy God, they will not believe in truth until they make you judge of what is in dispute between them and find within themselves no dislike of that which you decide, and submit with full submission" (Al-Nisaa 4/65).
The verse that proves that the source of sunnah is the revelation is an important evidence of al-i‘tisam. It has been interpreted that the following verse also includes the sunnah: "Nor does he speak of his own desire" (Al-Najm 53/3).
Prophet Muhammad's mission of revealing the Quran requires al-i‘tisam to his words and actions that are not related with the Quran. The Quran clearly presents the Prophet as a role model for Muslims, because Islam evaluates all parts and aspects of human life together. The duties of Prophet Muhammad naturally require the existence of his sunnah. Prophet Muhammad has the authority of a lawmaker. Moreover, the fact that sunnah is based on the revelation and it is approved of by the revelation is an indication that the source of the sunnah is the revelation. The fact that the Quran prohibits opposition to Prophet Muhammad or disobedience to his orders indicates the source of the sunnah and requires that obedience be given to the sunnah, which is not only the command of the Prophet, but the command of Allah.