All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
We have not come across any narrated texts or quotes from the prominent scholars which indicate that the Prophet saw the Throne of his Lord, blessed be He, while he was on earth. We are not aware of anyone who said this.
However, some scholars stated this in the events of the journey of the Mi'raaj (ascension) of the Prophet to the heavens. Some fabricated and rejected ahaadeeth, which Ibn Al-Jawzi cited in his book of Al-Mawdhoo'aat and As-Suyooti cited in Al-La’aali’ Al-Masnoo‘ah, were reported about this. Besides, Al-Albaani mentioned some of them in As-Silsilah Adh-Dha‘eefah, like the following hadeeth: “During my Night Journey, I saw written in the leg of the Throne: La ilaaha illa Allah Muhammadun Rasoolullah (There is nothing worthy of worship but Allah, Muhammad is the Messenger of Allah)...” Al-Albaani said, “It is a fabricated hadeeth (4902).”
Among the scholars who declared this is Imaam Al-Barbahaari, who wrote in the book Sharh As-Sunnah, “Among the requisites of belief is to believe that the Prophet ascended to the heavens until he reached the Throne, and Allah, most Exalted and Most High, spoke to him, and he entered Paradise and saw Hellfire, he saw the angels, and the Prophets were resurrected for him, and he saw the pavilions of the Throne and the Kursi and all that is in the heavens and in the earths, while he was awake (not in a dream).”
Other scholars denied this or at least did not confirm it because it is part of the Unseen, and nothing can be proven regarding it except with valid evidence. It is for this reason that Shaykh Abdul Azeez Ar-Raajihi commented on the previous statement of Imaam Al-Barbahaari, saying, “This needs evidence.”
Shaykh Radhiyy Ad-Deen Al-Qazweeni, may Allah have mercy on him, was asked about the Prophet stepping on the Throne with his sandal and the Lord saying to him, “The Throne was honored by your sandal, O Muhammad,” was this confirmed or not? He replied as follows, “As for the hadeeth of the Prophet stepping with his sandal on the Throne, then it is not authentic; rather, his reaching the uppermost part of the Throne was not confirmed, neither in a Saheeh (sound) nor a Hasan (good) narration, to begin with. What was confirmed in the religious texts to be authentic is that he only reached the Lote Tree of the Utmost Boundary (Sidrat Al-Muntaha). As regards going beyond it, then it is not authentic; rather, this is only narrated in Dha‘eef (weak) or Munkar (rejected) ahaadeeth.”
In brief, the Prophet having seen the Throne in his journey of Ascension to the heavens is something that is probable, but since this is not proven with authentic evidence, then the correct course of action is to not confirm it and remain neutral about it.
Allah knows best.