What is sunnah? What is sunnah definition?
All of the prophets were people who submitted to Allah, may He be glorified and exalted; they were chosen in order to guide human beings and to teach them how to fully submit to God. Although the prophets were chosen from different places, at different times throughout human history and they conveyed their message to people in various languages, their mission was the one and the same. Expounding upon this universality of the prophets and his role within it, the Prophet Muhammad (peace and blessings be upon him) said: “The similitude of mine and that of the Apostles before me is that of a person who built a house quite imposing and beautiful, but for one brick in one of its corners. People would go round it, appreciating the building, but saying: Why has the brick not been fixed here? He said: I am that brick and I am the last of the Apostles.” Allah, may He be glorified and exalted, prescribed that the example of perfect faith, is the belief in Him and then in His Messenger. For if a person believes only in [God] and not in His Messenger, they cannot be described as one who has perfect faith’; they must have faith in His Messenger together with Him… God has imposed the duty upon men and women to obey His divine communications, as well as, follow the Sunnah of His Messenger.
The term ‘Sunnah’ is an Arabic word, which, in pre-Islamic times, linguistically meant, ‘path’ or ‘custom’ relating to the norms and the practices of an individual or a people. During Prophet Muhammad’s (peace and blessings be upon him) own life time, the Sunnah began to be understood exclusively as the way of the Prophet, embodied in what he said, did, and what he approved of through explicit or tacit confirmation. Narrations regarding his physical appearance and his attributes were also included in hadith collections. In scholarship, ‘hadith’ is described as the verbal expression of the Prophet’s Sunnah. Hence, for example, the manner in which to perform various acts of worship mentioned in the Qur’an, such as, ritual prayer, fasting, charity and pilgrimage etcetera are learnt by Muslims from the hadith and practice of the Prophet. Muslims scholars have always appealed to the Sunnah as the second source of Islam after the Noble Qur’an. The Prophet’s way (Sunnah) can be found across the total spectrum of Shari`ah, from the obligatory (wājib) to the forbidden (hārām). This Sunnah is preserved in both the Qur’an and the Hadith. The term Sunnah is further utilized for two auxiliary purposes; it is utilized by legal theorists in jurisprudence to denote acts of worship that are not obligatory in Islam, but are recommended (mandūb) and it is also utilized to refer to the textual source of Hadith, in contrast with the Book (the Qur’an).  Hence, the Sunnah is the way of the Prophet and in general has been understood by Muslims to mean the imitation of the precedents set by the Prophet. “It is reported that Yazid ibn Yabnus said, ‘We went to Aisha and said, ‘Umm al-Muminin, what was the character of the Messenger of Allah like?’ She replied, ‘His character was the Qur’an’.”
It is evident that the Sunnah, as a whole, is binding in Islam. In the Qur’an it is stated, “It is not fitting for a Believer, man or woman, when a matter has been decided by Allah and His Messenger to have any option about their decision: if any one disobeys Allah and His Messenger, he is indeed clearly on a wrong Path.” The Prophet (peace and blessings be upon him) even warned his followers from establishing rulings in religion by willfully ignoring universal principles brought by the Sunnah, and, instead claim that the Qur’an is enough for them. He (peace and blessings be upon him) said, “Let me not find one of you reclining on his couch when he hears something regarding me which I have commanded or forbidden and saying: We do not know. We follow (only) what we found in Allah’s Book.” Therefore, the Sunnah is an indispensable part of religion and in this respect; one cannot refer to the Qur’an without the Sunnah, just as one cannot consider the Sunnah without the Qur’an.
Nevertheless, it is important for the new Muslim to recognize that the Sunnah is not the equivalent of the Qur’an in terms of its significance; in other words, the Qur’an is binding in all its totality, regarding its various commandments and injunctions. In contrast, the Sunnah due to its very nature is not binding in its entirety. For example, the hadith concerning matters, such as, law, ritual prayer, fasting, pilgrimage and almsgiving etcetera are binding, due to the fact that statements by the Prophet (peace and blessings be upon him), regarding such matters are related to his task of prophethood (risala). Whereas, his statements regarding fields that require specialist expertise, such as, agriculture, trade, treatment of diseases, art, etcetera are not mandatory unless they contain a divine message. In addition, the Prophet’s personal actions carried out as a human being, such as, his habits regarding eating, drinking, dressing, sleeping etcetera are not binding, however, Muslims should recognize that such actions of the Prophet constitute a high ethical and moral code of conduct and should be incorporated in their own lives.
Finally, the new Muslim should keep these following three Prophetic traditions in mind concerning the Sunnah: “He who does not follow my tradition in religion is not from me.” “Whoever revives my Sunnah has loved me, and whosoever loved me, he shall be with me in Paradise”, and, “There are three qualities for which anyone who is characterized by them will relish the sweetness of faith: He to whom Allah and His Messenger are dearer than all else; He who loves another human being for Allah’s sake alone; and He who has as great an abhorrence of returning to unbelief after Allah has rescued him from it as he has of being cast into Hell.”
 Sahih al-Bukhari, Book 43, Hadith 24.. i.e. meaning an act that is rewarded for in the afterlife, however not doing such an act (mandūb/Sunnah) is not punished. In this context in Islamic Law it is contrasted with the obligatory act which is rewarded for in the next life and not acting on it leads to punishment in the next life. . i.e. it is synonymous with Hadith, and distinguish evidence from that of the Qur’an. However, it is important to note that rulings of what is obligatory (Farḍ/Wājib) and recommended (Sunnah/mandūb) are found both in the Qur’an as well as in the Hadith.. Sahih al-Bukhari, 14: 308.. Q. 33: 36..Abu Dawud, Sunnah, 5; Al-Tirmidhi, Ilm, 107]. For further detail reading about the Sunnah and hadith please read E. M. Yaşaroğlu, İ. Erkul and N. Morgül, Hadith, Istanbul: Erkam Publications, 2016. Sahih al-Bukhari, Nikah, 1; Muslim, Nikah, 5.Sahih al-Tirmidhi, Ilm, 16.Sahih al-Bukhari, Iman 9, 14; Muslim, Iman 67
Source: Islam For New Muslims An Educational Guide,Assoc. Prof. Amjad M. Hussain, Erkam Publications