Praise be to Allaah.
Proof of the importance of the Sunnah
(1) The Qur’aan speaks of the importance of the Sunnah, for example:
(a) Allaah says (interpretation of the meaning): “He who obeys the Messenger has indeed obeyed Allaah . . .” [al-Nisaa’ 4:80] Allaah described obedience to the Prophet (peace be upon him) as being a part of obedience to Him. Then He made a connection between obedience to Him and obedience to the Prophet (peace be upon him): “O you who believe! Obey Allaah and obey the Messenger . . .” [al-Nisaa’ 4:59]
(b) Allaah warns us not to go against the Prophet (peace be upon him), and states that whoever disobeys him will be doomed to eternal Hell. Allaah says (interpretation of the meaning): “. . . And let those who oppose the Messenger’s commandment beware, lest some fitnah (trial, affliction, etc.) befall them or a painful torment be inflicted on them.” [al-Nur 24:63]
(c) Allaah has made obedience to His Prophet a religious duty; resisting or opposing it is a sign of hypocrisy: “But no, by your Lord, they can have no Faith, until they make you [Muhammad] judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission.” [al-Nisaa’ 4:65]
(d) Allaah commands His slaves to respond to Him and His Messenger: “O you who believe! Answer Allaah (by obeying Him) and (His) Messenger when he calls you to that which will give you life . . .” [al-Anfaal 8:24]
(e) Allaah also commands His slaves to refer all disputes to him: “. . . (And) if you differ in anything amongst yourselves, refer it to Allaah and His Messenger . . .” [al-Nisaa’ 4:59]
(2) The Sunnah itself indicates the importance of the Sunnah. For example:
(a) Al-Tirmidhi reported from Abu Raafi’ and others that the Prophet (peace be upon him) said: “I do not want to see any one of you reclining on his couch and, when he hears of my instructions or prohibitions, saying ‘I don’t accept it; we didn’t find any such thing in the Book of Allaah.’” Abu ‘Eesaa said: This is a saheeh hasan hadeeth. (See Sunan al-Tirmidhi, Shaakir edition, no. 2663).
Al-’Irbaad ibn Saariyah, may Allaah be pleased with him, reported that the Prophet (peace be upon him) said: “Would any of you think, reclining on his couch, that Allaah would only describe what is forbidden in the Qur’aan? I tell you, by Allaah, that I have warned and commanded and prohibited things that are as important as what is in the Qur’aan, if not more so.” (Reported by Abu Dawud, Kitaab al-Khiraj wa’l-imaarah wa’l-fay’).
(b) Abu Dawud also reported from al-’Irbaad ibn Saariyah, may Allaah be pleased with him, that “the Messenger of Allaah (peace be upon him) led us in prayer one day, then he turned to us and exhorted us strongly . . . (he said), ‘Pay attention to my sunnah (way) and the way of the Rightly-guided Khaleefahs after me, adhere to it and hold fast to it.’” (Saheeh Abi Dawud, Kitaab al-Sunnah).
(3) The scholars’ consensus (ijmaa’) affirming the importance of the Sunnah.
Al-Shaafi’i, may Allaah have mercy on him, said: “I do not know of anyone among the Sahaabah and Taabi’een who narrated a report from the Messenger of Allaah (peace be upon him) without accepting it, adhering to it and affirming that this was sunnah. Those who came after the Taabi’een, and those whom we met did likewise: they all accepted the reports and took them to be sunnah, praising those who followed them and criticizing those who went against them. Whoever deviated from this path would be regarded by us as having deviated from the way of the Companions of the Prophet (peace be upon him) and the scholars who followed them, and would be considered as one of the ignorant.
(4) Common sense indicates the importance of the Sunnah.
The fact that the Prophet (peace be upon him) is the Messenger of Allaah indicates that we must believe everything he said and obey every command he gave. It goes without saying that he has told us things and given instructions in addition to what is in the Qur’aan. It is futile to make a distinction between the Sunnah and the Qur’aan when it comes to adhering to it and responding to it. It is obligatory to believe in what he has told us, and to obey his instructions.
Islam Q&A: Fatwa 604
Sheikh Muhammed Salih Al-Munajjid