Zaqqum/ Cursed Tree:-

       The name of this tree appears only in the Quran and no where else in the Arabic language or any other language. There is absolutely no doubt that it was one of Muhammad's INVENTED words.

17: 60         Behold! We told thee that thy Lord doth encompass mankind round about: We granted the Vision which We showed thee but as a trial for men  as also the Cursed Tree (mentioned) in the Qur'an: We put terror (and warning) into them but it only increases their inordinate transgression!                       

       # The reference may be to lxxii. 28, probably an earlier Makkan revelation. But the argument is independent of time. This verse falls naturally into three divisions. Warnings and Portents and Signs are sent or not sent according to Allah's All-Wise Plan of Mercy and Justice, this is in no wise inconsistent with the apparent freedom given to the wicked: because (1) in any case Allah is all round all His creatures, and His delay as a Sign of Mercy in no way diminishes His power; (2) the Visions of Truth vouchsafed to Prophets of Allah are themselves Signs by which they can warn the ungodly; and (3) sometimes it is more merciful to give them time by not immediately bringing the matter to judgment. (17.60)

2250        The tree Zaqqum, a bitter and pungent tree described as growing at the bottom of Hell, a type of all that is disagreeable. See xxxvii. 62-65; xliv. 43-46; and lvi. 52. All these are Suras chronologically earlier than this Sura. The application of the name to a tree of the myrobalan kind in the region of Jericho is, I think, of post-Quranic date. It is a trial for wrong-doers. See xxxvii. 63 and n. 4073. (17.60)#       

37: 62        Is that the better entertainment or the Tree of Zaqqum?
       63        For We have truly made it (as) a trial for the wrongdoers.
      64        For it is a tree that springs out of the bottom of Hell Fire:
       65        The shoots of its fruit-stalks are like the heads of devils:

44: 43       Verily the tree of Zaqqum
      44       Will be the food of the Sinful
      45        Like molten brass; it will boil in their insides
       46        Like the boiling of scalding water.

      *** Suhayli, p228, has an interesting note to the effect that this wird is of Yamani origin, and there, it means anything which causes vomiting ***
56: 52        "Ye will surely taste of the Tree of Zaqqum.
      53        "Then will ye fill your insides therewith
       54        "And drink Boiling Water on top of it:
       55        "Indeed ye shall drink like diseased camels raging with thirst!

Sahih Al-Bukhari HadithHadith 5.228        Narrated byIbn Abbas
Regarding the Statement of Allah"
"And We granted the vision (ascension to the heavens) which We made you see (as an actual eye witness) was only made as a trial for the people."  (17.60)
Ibn Abbas added: The sights which Allah's Apostle was shown on the Night Journey when he was taken to Bait-ul-Maqdis (i.e. Jerusalem) were actual sights, (not dreams). And the Cursed Tree (mentioned) in the Qur'an is the tree of Zaqqum (itself).

Sahih Al-Bukhari HadithHadith 6.240        Narrated byIbn Abbas
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 eye-witness which was shown to Allah's Apostle 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).

Sahih Al-Bukhari HadithHadith 8.610        Narrated byIbn Abbas
(regarding the Verse) "And We granted the vision (Ascension to the heavens "Miraj") which We showed you (O Muhammad as an actual eye witness) but as a trial for mankind." (17.60):  Allah's Apostle actually saw with his own eyes the vision (all the things which were shown to him) on the night of his Night Journey to Jerusalem (and then to the heavens). The cursed tree which is mentioned in the Qur'an is the tree of Az-Zaqqum.