Allah Almighty has commanded obedience in the Holy Quran to what has been revealed by Him, and this is called Divine Revelation, which is only the Holy Quran.
First Point
Every Muslim should know that the Sunnah of the Prophet ﷺ, whether actions or sayings, is the second type of Divine Revelation that was revealed to the Noble Messenger ﷺ, and the first type of revelation is certainly the Holy Quran. Allah, Glorified and Exalted, says:
وَمَا يَنْطِقُ عَنِ الْهَوَى إِنْ هُوَ إِلَّا وَحْيٌ يُوحَى
Reference: (An-Najm: 3-4)
Translation: And he (the Prophet) does not speak from his own desire; it is only a revelation that is revealed.
From this verse, it is understood that the Prophet ﷺ did not speak without revelation, and every sensible person realizes that during his blessed life, besides the Holy Quran, he used to guide the Companions, so according to the Quran, that speech of his will be included in the category of revelation.
Imam Qurtubi states in the interpretation of this verse that it is evidence that the Sunnah, like revelation, is sent down from Allah Almighty.
Reference: (Al-Jami' li Ahkam al-Qur'an: 17/85)
Thus, the Sunnah is also revelation, and there is consensus among all the Companions, the Followers, and the Ahl al-Sunnah on this, and it is conveyed by the Messenger of Allah ﷺ. See:
Reference: Al-Ahkam by Ibn Hazm (1/95)
.Second Point
Allah Almighty says:
إِنَّا أَوْحَيْنَا إِلَيْكَ كَمَا أَوْحَيْنَا إِلَى نُوحٍ وَالنَّبِيِّينَ مِنْ بَعْدِهِ
Reference: (An-Nisa: 163)
Translation: Indeed, We have revealed to you, [O Muhammad], as We revealed to Noah and the prophets after him...
From the mentioned verse, it is understood that revelation was also sent to Prophet Noah (peace be upon him) and other prophets, which was not all in the form of a book, and the revelation that Allah Almighty sent down upon the Prophet ﷺ was the Glorious Qur'an, and besides that, because the blessed verse states that We revealed to you in the same manner as We revealed to those before you.
Similarly, Allah Almighty said:
وَمَا كَانَ لِبَشَرٍ أَنْ يُكَلِّمَهُ اللَّهُ إِلَّا وَحْيًا أَوْ مِنْ وَرَاءِ حِجَابٍ أَوْ يُرْسِلَ رَسُولًا فَيُوحِيَ بِإِذْنِهِ مَا يَشَاءُ
Reference: (Ash-Shura: 51)
Translation: And it is not possible for any human being that Allah should speak to him except through revelation, or from behind a veil, or that He sends a messenger and then reveals by His command whatever He wills.
This verse mentions the types of revelation, describing three types, and the revelation of the Holy Quran corresponds to only one of these types. The other two mentioned types indicate that besides the Quran, there is also revelation, and that revelation is the Sunnah.
Third Point
Allah Almighty says:
وَأَنْزَلَ اللَّهُ عَلَيْكَ الْكِتَابَ وَالْحِكْمَةَ وَعَلَّمَكَ مَا لَمْ تَكُنْ تَعْلَمُ
Reference: (An-Nisa:113)
Translation: And Allah has sent down to you the Book and wisdom and taught you that which you did not know.
In the mentioned verse, describing wisdom as something sent down indicates that it is not merely a matter of intellect and knowledge, but that this wisdom refers to something else, which is the Sunnah. Thus, it is established that the Sunnah, like the Quran, is also revealed.
Fourth Point
Allah Almighty, regarding His Prophet ﷺ and the conveyance of the religion, says:
وَلَوْ تَقَوَّلَ عَلَيْنَا بَعْضَ الاْقَاوِيلِ (44) لاَخَذْنَا مِنْهُ بِالْيـَمِينِ(45)ثُمَّ لَقَطَعْنَا مِنْهُ الْوَتِينَ (46) فَمَا مِنكُم مِّنْ أَحَد عَنْهُ حَـجِزِينَ
Reference: (Al-Haqqah:46)
Translation: And if he had fabricated against Us some sayings, We would have certainly seized him by the right hand; then indeed, We would have cut off his aorta.
From this noble verse, it is understood that if you ﷺ were to teach something contrary to the revelation, which is impossible, then Allah, the Lord of Glory, is capable of seizing you, and the consequence of that has also been mentioned.
So, after such a severe warning, can it be expected that you ﷺ would independently declare anything lawful or unlawful in the religion? Therefore, the belief of Muslims is that all your ﷺ sayings and actions were subject to the pleasure of Allah, which is only possible through divine revelation.
Fifth Point
The Companions, may Allah be pleased with them all, acted upon your ﷺ commands and were not subjected to any kind of punishment for it; rather, they attained success. The Quran praises their following of this, indicating that acting upon the Sunnah is indeed the pleasure of Allah. So if the Sunnah was not revelation, how could this be possible?!
Sixth Point
Revelation is not limited only to the Holy Quran, because in most verses of the Holy Quran, there is mention of certain matters and rulings to which the Quran alludes but are not explicitly mentioned in the Quran, as Allah Almighty says:
مَا قَطَعْتُمْ مِنْ لِينَةٍ أَوْ تَرَكْتُمُوهَا قَائِمَةً عَلَى أُصُولِهَا فَبِإِذْنِ اللَّهِ
Reference: (Al-Hashr:5)
Translation: Whatever palm trees you cut down or left standing on their roots, it was by Allah’s permission and so that He might disgrace the transgressors.
When the trees were cut and burned, the Jews and hypocrites raised an outcry that Muhammad (peace be upon him) was cutting down trees and committing corruption on earth, while he claimed to be reforming. In response, Allah Almighty reassured the Muslims that whatever tree you cut down or left standing on its roots, all of this was by Allah's permission. This means that although the general rule during war is to avoid burning and cutting trees and crops, on this occasion, the trees that were burned, cut, or left standing were all by Allah's permission, so there is no need to be troubled by the opponents' words.
Is this permission mentioned in the Quran? If not, then it indicates that there is revelation besides the Quran, which is in the form of Hadith.
