Sahih al-Bukhari 4716
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · "And We made not the vision which We showed you (O Muḥammad [pbuh] as an actual eye-witness and not as a dream on the night of Al-Isrā') , but a trial for mankind..." (V.17:60)
Narrated Ibn `Abbas:
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ ، حَدَّثَنَا سُفْيَانُ ، عَنْ عَمْرٍو ، عَنْ عِكْرِمَةَ ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنه ـ {وَمَا جَعَلْنَا الرُّؤْيَا الَّتِي أَرَيْنَاكَ إِلاَّ فِتْنَةً لِلنَّاسِ} قَالَ هِيَ رُؤْيَا عَيْنٍ أُرِيَهَا رَسُولُ اللَّهِ صلى الله عليه وسلم لَيْلَةَ أُسْرِيَ بِهِ {وَالشَّجَرَةَ الْمَلْعُونَةَ} شَجَرَةُ الزَّقُّومِ.
Regarding: 'And We granted the vision (Ascension to the Heaven "Miraj") which We showed you (O Muhammad as an actual eye witness) but as a trial for mankind.' (17.60) It was an actual eyewitness which was shown to Allah's Messenger (ﷺ) during the night he was taken on a journey (through the heavens). And the cursed tree is the tree of Az-Zaqqum (a bitter pungent tree which grows at the bottom of Hell).