Muhammad was never authorized to explain the Quran. The Quran actually tells Muhmmad to refrain from explaining the Quran.
[75:16] Do not move your tongue to hasten it.
[75:17] It is we who will collect it into Quran.
[75:18] Once we recite it, you shall follow such a Quran.
[75:19] Then it is we who will explain it.
(٧٥:١٦) لَا تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ
(٧٥:١٧) إِنَّ عَلَيْنَا جَمْعَهُ وَقُرْآنَهُ
(٧٥:١٨) فَإِذَا قَرَأْنَاهُ فَاتَّبِعْ قُرْآنَهُ
(٧٥:١٩) ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ
Verse 19 of Sura 75, uses the term “we” which constitutes that God will utilize help from other entities to carry out this act. In this case, this is achieved by sending a messenger after the prophet to explain the Quran.
[42:51] No human being can communicate with GOD except through inspiration, or from behind a barrier, or by sending a messenger through whom He reveals what He wills. He is the Most High, Most Wise.
وَمَا كَانَ لِبَشَرٍ أَنْ يُكَلِّمَهُ اللَّهُ إِلَّا وَحْيًا أَوْ مِنْ وَرَاءِ حِجَابٍ أَوْ يُرْسِلَ رَسُولًا فَيُوحِيَ بِإِذْنِهِ مَا يَشَاءُ إِنَّهُ عَلِيٌّ حَكِيمٌ
Some find it strange that Muhammad was not allowed to explain the Quran, but this narrative aligns with the verses of the Quran. The Quran was revealed over a span of 23 years; when the prophet was faced with a question or predicament, God would provide him the exact words the prophet was to say in response. This corresponds with the multitude of verses in the Quran where the prophet is specifically told to “say” in regards to specific questions or conditions that arose in the prophet’s life as they occurred.
[2:219] They ask you about intoxicants and gambling: say, “In them there is a gross sin, and some benefits for the people. But their sinfulness far outweighs their benefit.” They also ask you what to give to charity: say, “The excess.” GOD thus clarifies the revelations for you, that you may reflect,
يَسْأَلُونَكَ عَنِ الْخَمْرِ وَالْمَيْسِرِ قُلْ فِيهِمَا إِثْمٌ كَبِيرٌ وَمَنَافِعُ لِلنَّاسِ وَإِثْمُهُمَا أَكْبَرُ مِنْ نَفْعِهِمَا وَيَسْأَلُونَكَ مَاذَا يُنْفِقُونَ قُلِ الْعَفْوَ كَذَٰلِكَ يُبَيِّنُ اللَّهُ لَكُمُ الْآيَاتِ لَعَلَّكُمْ تَتَفَكَّرُونَ
[6:145] Say, “I do not find in the revelations given to me any food that is prohibited for any eater except: (1) carrion, (2) running blood, (3) the meat* of pigs, for it is contaminated, and (4) the meat of animals blasphemously dedicated to other than GOD.” If one is forced (to eat these), without being deliberate or malicious, then your Lord is Forgiver, Most Merciful.
قُلْ لَا أَجِدُ فِي مَا أُوحِيَ إِلَيَّ مُحَرَّمًا عَلَىٰ طَاعِمٍ يَطْعَمُهُ إِلَّا أَنْ يَكُونَ مَيْتَةً أَوْ دَمًا مَسْفُوحًا أَوْ لَحْمَ خِنْزِيرٍ فَإِنَّهُ رِجْسٌ أَوْ فِسْقًا أُهِلَّ لِغَيْرِ اللَّهِ بِهِ فَمَنِ اضْطُرَّ غَيْرَ بَاغٍ وَلَا عَادٍ فَإِنَّ رَبَّكَ غَفُورٌ رَحِيمٌ
The idea that Muhammad did not explain the Quran is further reinforced in the following verse regarding the criticisms that were hurled at him for only listening.
[9:61] Some of them hurt the prophet by saying, “He is all ears!” Say, “It is better for you that he listens to you. He believes in GOD, and trusts the believers. He is a mercy for those among you who believe.” Those who hurt GOD’s messenger have incurred a painful retribution.
وَمِنْهُمُ الَّذِينَ يُؤْذُونَ النَّبِيَّ وَيَقُولُونَ هُوَ أُذُنٌ قُلْ أُذُنُ خَيْرٍ لَكُمْ يُؤْمِنُ بِاللَّهِ وَيُؤْمِنُ لِلْمُؤْمِنِينَ وَرَحْمَةٌ لِلَّذِينَ آمَنُوا مِنْكُمْ وَالَّذِينَ يُؤْذُونَ رَسُولَ اللَّهِ لَهُمْ عَذَابٌ أَلِيمٌ
From this verse, it is clear that some were upset that the prophet was just listening as opposed to actively engaging with the people in conversation. This is because he was listening to what God wanted him to say in regards to matters and not speaking of his own volition. This trait of the prophet is again addressed in the following verse.
[33:53] O you who believe, do not enter the prophet’s homes unless you are given permission to eat, nor shall you force such an invitation in any manner. If you are invited, you may enter. When you finish eating, you shall leave; do not engage him in lengthy conversations (Hadith). This used to hurt the prophet, and he was too shy to tell you. But GOD does not shy away from the truth. If you have to ask his wives for something, ask them from behind a barrier. This is purer for your hearts and their hearts. You are not to hurt the messenger of GOD. You shall not marry his wives after him, for this would be a gross offense in the sight of GOD.
يَاأَيُّهَا الَّذِينَ آمَنُوا لَا تَدْخُلُوا بُيُوتَ النَّبِيِّ إِلَّا أَنْ يُؤْذَنَ لَكُمْ إِلَىٰ طَعَامٍ غَيْرَ نَاظِرِينَ إِنَاهُ وَلَٰكِنْ إِذَا دُعِيتُمْ فَادْخُلُوا فَإِذَا طَعِمْتُمْ فَانْتَشِرُوا وَلَا مُسْتَأْنِسِينَ لِحَدِيثٍ إِنَّ ذَٰلِكُمْ كَانَ يُؤْذِي النَّبِيَّ فَيَسْتَحْيِي مِنْكُمْ وَاللَّهُ لَا يَسْتَحْيِي مِنَ الْحَقِّ وَإِذَا سَأَلْتُمُوهُنَّ مَتَاعًا فَاسْأَلُوهُنَّ مِنْ وَرَاءِ حِجَابٍ ذَٰلِكُمْ أَطْهَرُ لِقُلُوبِكُمْ وَقُلُوبِهِنَّ وَمَا كَانَ لَكُمْ أَنْ تُؤْذُوا رَسُولَ اللَّهِ وَلَا أَنْ تَنْكِحُوا أَزْوَاجَهُ مِنْ بَعْدِهِ أَبَدًا إِنَّ ذَٰلِكُمْ كَانَ عِنْدَ اللَّهِ عَظِيمًا
It is worth pointing out that the word for conversation in the above verse is “hadith”. This shows that the prophet did not like discussing Hadith besides the Quran.
Not only was Muhammad not authorized to explain the Quran, but his followers also were not authorized to collect his Hadith to form another set of laws to rival the Quran.
[6:112] We have permitted the enemies of every prophet—human and jinn devils—to inspire in each other fancy words, in order to deceive. Had your Lord willed, they would not have done it. You shall disregard them and their fabrications.
وَكَذَٰلِكَ جَعَلْنَا لِكُلِّ نَبِيٍّ عَدُوًّا شَيَاطِينَ الْإِنْسِ وَالْجِنِّ يُوحِي بَعْضُهُمْ إِلَىٰ بَعْضٍ زُخْرُفَ الْقَوْلِ غُرُورًا وَلَوْ شَاءَ رَبُّكَ مَا فَعَلُوهُ فَذَرْهُمْ وَمَا يَفْتَرُونَ
[6:113] This is to let the minds of those who do not believe in the Hereafter listen to such fabrications, and accept them, and thus expose their real convictions.
(١١٣) وَلِتَصْغَىٰ إِلَيْهِ أَفْئِدَةُ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ وَلِيَرْضَوْهُ وَلِيَقْتَرِفُوا مَا هُمْ مُقْتَرِفُونَ
[6:114] Shall I seek other than GOD as a source of law, when He has revealed to you this book fully detailed? Those who received the scripture recognize that it has been revealed from your Lord, truthfully. You shall not harbor any doubt.
أَفَغَيْرَ اللَّهِ أَبْتَغِي حَكَمًا وَهُوَ الَّذِي أَنْزَلَ إِلَيْكُمُ الْكِتَابَ مُفَصَّلًا وَالَّذِينَ آتَيْنَاهُمُ الْكِتَابَ يَعْلَمُونَ أَنَّهُ مُنَزَّلٌ مِنْ رَبِّكَ بِالْحَقِّ فَلَا تَكُونَنَّ مِنَ الْمُمْتَرِينَ
[6:115] The word of your Lord is complete, in truth and justice. Nothing shall abrogate His words. He is the Hearer, the Omniscient.
(١١٥) وَتَمَّتْ كَلِمَتُ رَبِّكَ صِدْقًا وَعَدْلًا لَا مُبَدِّلَ لِكَلِمَاتِهِ وَهُوَ السَّمِيعُ الْعَلِيمُ
[6:116] If you obey the majority of people on earth, they will divert you from the path of GOD. They follow only conjecture; they only guess.
(١١٦) وَإِنْ تُطِعْ أَكْثَرَ مَنْ فِي الْأَرْضِ يُضِلُّوكَ عَنْ سَبِيلِ اللَّهِ إِنْ يَتَّبِعُونَ إِلَّا الظَّنَّ وَإِنْ هُمْ إِلَّا يَخْرُصُونَ