Short answer
Manna is the food Allah sent down to the Children of Israel in the wilderness after Moses led them out of Egypt. Both the Bible and the Quran mention it, and the Quran pairs it with quails: al-mann wa al-salwa. Muslims see it as one of Allah's gifts to them, and the Prophet ﷺ said truffles are a kind of manna.
There is no fiqh ruling here. Muslims believe in this miracle as the Quran describes it, and do not need to settle exactly what manna was.
The four schools agree on this.
Explanation
In the Bible, manna appears in the book of Exodus. The Israelites, hungry in the desert, found a fine white substance on the ground each morning except the Sabbath, described as like coriander seed and tasting like wafers made with honey. They gathered it daily for forty years. The name is usually explained from the Hebrew question what is it?
The Quran mentions the same gift three times. Allah reminds the Children of Israel that He shaded them with clouds and sent down to them manna and quails, saying: eat from the good things We have provided for you. This was during their years in the wilderness.
Muslim commentators describe manna as a sweet substance that settled on trees and the ground, eaten like honey or made into food, given without any farming or labour. The Prophet ﷺ said truffles are a kind of manna, which scholars explain as food Allah provides from the earth without anyone planting it.
The Quran also tells what happened next: the people grew tired of one food and asked Moses for herbs, cucumbers, garlic, lentils and onions. He asked: would you exchange what is better for what is less? For Muslims the lesson is gratitude for what Allah gives. See the story of Prophet Musa.
The evidence
Quran, Surah Al-Baqara 2:57
وَظَلَّلْنَا عَلَيْكُمُ ٱلْغَمَامَ وَأَنزَلْنَا عَلَيْكُمُ ٱلْمَنَّ وَٱلسَّلْوَىٰ ۖ كُلُوا۟ مِن طَيِّبَٰتِ مَا رَزَقْنَٰكُمْ ۖ وَمَا ظَلَمُونَا وَلَٰكِن كَانُوٓا۟ أَنفُسَهُمْ يَظْلِمُونَ ﴿٥٧﴾
And We shaded you with clouds and sent down to you manna and quails, [saying], "Eat from the good things with which We have provided you." And they wronged Us not - but they were [only] wronging themselves.
Allah fed the Children of Israel with manna and quails.
Quran, Surah Taa-Haa 20:80
يَٰبَنِىٓ إِسْرَٰٓءِيلَ قَدْ أَنجَيْنَٰكُم مِّنْ عَدُوِّكُمْ وَوَٰعَدْنَٰكُمْ جَانِبَ ٱلطُّورِ ٱلْأَيْمَنَ وَنَزَّلْنَا عَلَيْكُمُ ٱلْمَنَّ وَٱلسَّلْوَىٰ ﴿٨٠﴾
O Children of Israel, We delivered you from your enemy, and We made an appointment with you at the right side of the mount, and We sent down to you manna and quails,
A second mention of the same gift.
Quran, Surah Al-Baqara 2:61
وَإِذْ قُلْتُمْ يَٰمُوسَىٰ لَن نَّصْبِرَ عَلَىٰ طَعَامٍۢ وَٰحِدٍۢ فَٱدْعُ لَنَا رَبَّكَ يُخْرِجْ لَنَا مِمَّا تُنۢبِتُ ٱلْأَرْضُ مِنۢ بَقْلِهَا وَقِثَّآئِهَا وَفُومِهَا وَعَدَسِهَا وَبَصَلِهَا ۖ قَالَ أَتَسْتَبْدِلُونَ ٱلَّذِى هُوَ أَدْنَىٰ بِٱلَّذِى هُوَ خَيْرٌ ۚ ٱهْبِطُوا۟ مِصْرًۭا فَإِنَّ لَكُم مَّا سَأَلْتُمْ ۗ وَضُرِبَتْ عَلَيْهِمُ ٱلذِّلَّةُ وَٱلْمَسْكَنَةُ وَبَآءُو بِغَضَبٍۢ مِّنَ ٱللَّهِ ۗ ذَٰلِكَ بِأَنَّهُمْ كَانُوا۟ يَكْفُرُونَ بِـَٔايَٰتِ ٱللَّهِ وَيَقْتُلُونَ ٱلنَّبِيِّۦنَ بِغَيْرِ ٱلْحَقِّ ۗ ذَٰلِكَ بِمَا عَصَوا۟ وَّكَانُوا۟ يَعْتَدُونَ ﴿٦١﴾
And [recall] when you said, "O Moses, we can never endure one [kind of] food. So call upon your Lord to bring forth for us from the earth its green herbs and its cucumbers and its garlic and its lentils and its onions." [Moses] said, "Would you exchange what is better for what is less? Go into [any] settlement and indeed, you will have what you have asked." And they were covered with humiliation and poverty and returned with anger from Allah [upon them]. That was because they [repeatedly] disbelieved in the signs of Allah and killed the prophets without right. That was because they disobeyed and were [habitually] transgressing.
The lesson of ingratitude for Allah's provision.
Sahih al-Bukhari 4478
Sahih... الكمأة من المن وماؤها شفاء للعين ...
"Truffles are a kind of manna, and their water is a cure for the eye."
The Prophet ﷺ linked manna to food Allah provides without effort.
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.