Bismillah.
لَا شَرِيكَ لَهُ ۖ وَبِذَٰلِكَ أُمِرْتُ وَأَنَا أَوَّلُ الْمُسْلِمِينَ
He has no partner. I have been commanded to follow this creed and I am the first of those who submit [to Allah].
(Sūrat al-An‘ām, No. 6, Āyat 163)
A few verses of the Quran refer to the Prophet of Islam sallallāhu ‘alayhi wa-ālihi wasallam as the first Muslim. There are different interpretations of what this means:
1) Some scholars like Shaykh Tabarsī believe that it refers to the fact that he was the first of those who submitted from the final Ummah. Hence scholars of jurisprudence like Shaykh al-Tūsī say that when this verse (or similar ones) are recited in supplications, believers must replace, I am the first of those who submit with “I am of those who submit”.
2) Scholars like Mullah Fayz Kāshānī believe that the Prophet (s) was the first soul that submitted, in ‘Ālam al-Dharr. When the pledge was taken from human souls to take Allah ‘azza wajall as their Lord (see Q 7:172), the soul of the Prophet (s) was the first to accept the pledge and submit.
3) Allāmah Tabātabā’ī believes that the Prophet (s) was the first to attain the status of complete and perfect servitude according to the commands of Allah subhānahu wata‘ālā. He was thus the first human being to be a perfect servant of Allah in all aspects. The Quran only refers to him as being the first Muslim. Other Prophets are said to be from those who submit. About Prophet Ibrāhīm (a) Allah says: When his Lord said to him, ‘Submit,’ he said, ‘I submit to the Lord of all the worlds.’ (Q 2:131). Prophet Nūh (a) says: If you turn your back, I do not ask any reward from you; my reward lies only with Allah, and I have been commanded to be of those who submit. (Q 10:72)
The view of Allāmah Tabātabā’ī is widely accepted by most scholars today. The precedence in submission is not historical or in time. Otherwise, every Prophet would be considered the first of those who submit in their time.
Apart from the above verse, other verses of the Quran also refer to the Prophet (s) as the first of the Muslims. In the same surah Allah says: Say, ‘Shall I take for a guardian other than Allah, the originator of the heavens and the earth, who feeds and is not fed?’ Say, ‘I have been commanded to be the first of those who submit to Allah, and [told,] “Never be one of the polytheists. And in another verse: Say, ‘I have been commanded to worship Allah with exclusive faith in Him and I have been commanded to be the foremost of those who submit [to Him].’ (Q 39:11-12).
There are hadith that refer to Imam Ali ‘alayhis-salām as the first Muslim. The Prophet (s) is reported to have said: O Ali, you are the first to submit and the first to believe (Bihār al-Anwār, 40:78). This refers to Imam Ali (a) being the first to accept Islam at the hands of the Prophet (s).
May the Almighty help us recognize and appreciate the status of our Prophet (s). His outstanding qualities have been described in many places in the Quran. It befits us in this month of Rabi al-Awwal to ponder over these verses and learn more about him.
Sources : https://hawzah.net/fa/Article/View/97298