Tafsir of As-Saffat 37:63

Truly, We have made it (as) a trial for the wrongdoers. Qatadah said, "The tree of Zaqqum is mentioned as a test for those who are misguided. They said, `Your companion tells you that in the Fire there is a tree, but fire consumes trees.' Then Allah revealed the words:

إنها شجرة تخرج في أصل الجحيم