Short answer
Muslims do not know. The Quran says Allah sent a messenger to every nation and told the Prophet ﷺ the stories of only some of them, so a person not named in the Quran or hadith can be neither confirmed nor ruled out as a prophet. Some Muslim writers have suggested the Buddha may have been one, but that is speculation, and Muslims do not follow Buddhist teachings.
Belief is required in the prophets named in the Quran and in all of Allah's messengers in general. Declaring a particular unnamed person a prophet, or firmly denying it, without evidence is not allowed. Hanafi creed books warn against fixing the names or number of prophets beyond what is established.
The four schools agree on this.
Explanation
The Quran says "there was no nation but that there had passed within it a warner", and "We certainly sent into every nation a messenger, saying: Worship Allah and avoid false gods." It also says Allah told the Prophet ﷺ the stories of some messengers and not others. So Muslims believe there were prophets in India, China and everywhere else, most of them unnamed. See how many prophets are there?
Siddhartha Gautama, the Buddha, lived in northern India about five centuries before Jesus. His teachings were passed down orally and written by followers long after him. Some modern Muslim writers wondered whether he was an early prophet whose message was later changed, and a few even linked him to Dhul-Kifl in the Quran. These ideas have no evidence from the Quran or hadith, so Muslim scholars do not affirm them.
What Muslims can judge is the teaching itself. Buddhism as practised today does not centre on worship of one Creator God, which is the message of every prophet. So whatever the Buddha's own story, Muslims do not follow Buddhist practice. They can still recognise good values found among Buddhists, such as compassion and self-discipline.
Islam also teaches respect: Muslims must not insult what others hold sacred, and should treat Buddhist neighbours with kindness and justice. See what Islam says about other religions.
The evidence
Quran, Surah Faatir 35:24
إِنَّآ أَرْسَلْنَٰكَ بِٱلْحَقِّ بَشِيرًۭا وَنَذِيرًۭا ۚ وَإِن مِّنْ أُمَّةٍ إِلَّا خَلَا فِيهَا نَذِيرٌۭ ﴿٢٤﴾
Indeed, We have sent you with the truth as a bringer of good tidings and a warner. And there was no nation but that there had passed within it a warner.
Allah sent warners to every nation, many of them unnamed.
Quran, Surah Ghafir 40:78
وَلَقَدْ أَرْسَلْنَا رُسُلًۭا مِّن قَبْلِكَ مِنْهُم مَّن قَصَصْنَا عَلَيْكَ وَمِنْهُم مَّن لَّمْ نَقْصُصْ عَلَيْكَ ۗ وَمَا كَانَ لِرَسُولٍ أَن يَأْتِىَ بِـَٔايَةٍ إِلَّا بِإِذْنِ ٱللَّهِ ۚ فَإِذَا جَآءَ أَمْرُ ٱللَّهِ قُضِىَ بِٱلْحَقِّ وَخَسِرَ هُنَالِكَ ٱلْمُبْطِلُونَ ﴿٧٨﴾
And We have already sent messengers before you. Among them are those [whose stories] We have related to you, and among them are those [whose stories] We have not related to you. And it was not for any messenger to bring a sign [or verse] except by permission of Allah. So when the command of Allah comes, it will be concluded in truth, and the falsifiers will thereupon lose [all].
Many prophets are not named, so Muslims cannot confirm or deny unnamed figures.
Quran, Surah An-Nahl 16:36
وَلَقَدْ بَعَثْنَا فِى كُلِّ أُمَّةٍۢ رَّسُولًا أَنِ ٱعْبُدُوا۟ ٱللَّهَ وَٱجْتَنِبُوا۟ ٱلطَّٰغُوتَ ۖ فَمِنْهُم مَّنْ هَدَى ٱللَّهُ وَمِنْهُم مَّنْ حَقَّتْ عَلَيْهِ ٱلضَّلَٰلَةُ ۚ فَسِيرُوا۟ فِى ٱلْأَرْضِ فَٱنظُرُوا۟ كَيْفَ كَانَ عَٰقِبَةُ ٱلْمُكَذِّبِينَ ﴿٣٦﴾
And We certainly sent into every nation a messenger, [saying], "Worship Allah and avoid Taghut." And among them were those whom Allah guided, and among them were those upon whom error was [deservedly] decreed. So proceed through the earth and observe how was the end of the deniers.
Every true prophet called to the worship of Allah alone.
Where the ruling is recorded
- al-Aqa'id al-Nasafiyya, the section on the prophets. Advises believing in all the prophets without fixing a number, so as not to include or exclude wrongly.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.