The Arabic word “Sunnah” lexically means “road” or “practice.” In the language of the Prophet and the Companions, it denotes the whole of licit [lawful] practices followed in the Religion [dîn], particularly the pristine (hanîf) path of Prophets, whether pertaining to belief, religious and social practice, or ethics generally speaking. The importance of the Sunnah is first of all that it explains the Book of Allah (i.e The Creator) and is a commentary on it, then it adds some rulings to those in the Book of Allaah.
Allah says (interpretation of the meaning):
And We have also sent down unto you (O Muhammad) the Dhikr [reminder and the advice (i.e. the Qur’an)], that you may explain clearly to men what is sent down to them, and that they may give thought” [Quran.com/16/44].
Firstly, Sunnah mu’akkadah (confirmed Sunnah), naafil (supererogatory), voluntary and mandoob (recommended) all share a similar meaning; they are acts of worship that are enjoined and encouraged in Islam, without being obligatory. The one who does them will be rewarded but there is no sin on the one who does not do them.
That is like praying qiyaam al-layl (optional prayers at night), the sunan rawaatib (regular Sunnah prayers), starting on the right when putting on one’s clothes, and so on. Some of the scholars think that these words are similar in meaning, whilst others – like the Maalikis – differentiate between them. In their view “Sunnah” refers to something that the Prophet (blessings and peace of Allah be upon him) did persistently; naafil refers to things that he did sometimes and not at other times.
Secondly, The word “Sunnah” has two meanings:
the path of guidance, which is the meaning in many ahaadeeth, such as the words of the Prophet (peace and blessings of Allaah be upon him):
Whoever turns away from my Sunnah has nothing to do with me.”
What the scholars of usool and fiqh call “mustahabb (encouraged)”, which are deeds for which the one who does them will be rewarded, but the one who does not do them will not deserve to be punished for that. Examples include al-Sunan al-Rawaatib (Sunnah prayers which the Prophet (peace and blessings of Allaah be upon him) did regularly), Salaat al-Duhaa and so on.
Therefore, a person will not be punished for not doing things which are Sunnah in the second sense. With regard to the first definition, this is not the case, for these are divided into things which are obligatory (waajib) and things which are supererogatory (naafil).
Sunnat al-Fajr and al-Witr are Sunnah Mu’akkadah, prayer which the Prophet (peace and blessings of Allaah be upon him) never omitted to do, whether he was travelling or not.
Letting the beard grow is an obligation (waajib); it does not come under the category of Sunnah as defined by the fuqahaa’. Whoever shaves his beard is imitating the Majoos (Zoroastrians), going against the Fitrah (natural disposition of man), and changing the creation of Allaah.
The one who neglects an act that is an obligatory Sunnah will be punished; the one who neglects a mustahabb Sunnah will not be punished, but he is missing out on a great reward and the chance to make up any shortfall in his obligations (waajibaat), because on the Day of Resurrection, any shortfall in his obligations will be made up from his Sunnah actions, if he has any to his credit. Doing Sunnah actions is also a means of maintaining the practice of waajib actions.
The scholars also use the word “Sunnah” in contrast to bid’ah (reprehensible innovation) and say “Ahl al-Sunnah” (the people or followers of Sunnah) to distinguish them from the followers of misguided kaafir sects such as the Jahamiyyah, or innovators who are not kaafirs, such as the Ash’aris and others. The Sunnah in this sense has to be followed. Following the way of Ahl al-Sunnah is obligatory, and whoever departs from their way is doomed. Imaam Maalik (may Allaah have mercy on him) said: the Sunnah is like the ship of Nooh: whoever boards it will be saved and whoever stays behind will be drowned.
Thirdly, No doubt it is obligatory for the Muslim to be a follower of his Prophet (blessings and peace of Allah be upon him) in what he prescribed and it is not permissible for him to go against that or to introduce any innovation into the religion, because of the evidence that indicates that it is obligatory to follow and it is forbidden to introduce innovation. But it should be noted that differing from the way of the Prophet (blessings and peace of Allah be upon him) and falling into bid‘ah may mean one of two things: (1)introducing an act of worship for which there is no basis in Islam, such as touching graves and seeking help from their occupants. The scholars call this real innovation (al-bid‘ah al-haqeeqah). This is that which was not prescribed at all. (2)the act of worship may be originally prescribed in Islam, and what is contrary to the sunnah may have to do with defining a certain time or place for it, or a certain number of times it is to be repeated, or the manner in which it is to be done or the reason for which it is to be done. This is called innovation by addition (al-bid‘ah al-idaafiyyah); it is not bid‘ah unless it is done regularly and repeatedly. If it is done only once or twice without adhering to that, then it is not bid‘ah, such as if people pray qiyaam (night prayer) in congregation (jamaa‘ah) on some occasion, without thinking that there is any particular virtue in doing so.
To sum up,
It is essential that it be established in the mind and heart of every Muslim that the Sunnah – which is the words, deeds and approval that are attributed to the Prophet (peace and blessings of Allaah be upon him) – is one of the two parts of divine Revelation that were revealed to the Messenger of Allaah (peace and blessings of Allaah be upon him). The other part of the Revelation (Wahy) is the Holy Qur’aan.
Allaah says (interpretation of the meaning):
“Nor does he speak of (his own) desire.