Tafsir of Al-Waqi'ah 56:54

As for the masculine pronoun in this reading—His saying, Glorified is He: “Fa-sharibuna ‘alayhi” (Then you will drink upon it)—meaning, immediately thereafter without delay—(min al-hamim) (of boiling water)—meaning water that is at the extreme of heat due to overwhelming thirst—its meaning is manifest and does not require interpretation.

Some have said: The feminine was used first [in the previous verse] considering the meaning, and the masculine was used second considering the [grammatical] word. It is said regarding “‘alayhi”: Indeed, it involves considering the word after having considered the meaning, which is contrary to convention. If the masculine pronoun had been returned to the "tree" (al-shajar) considering it as "that which is eaten" (ma’kul), such that both the masculine and feminine were based on the meaning, it would have been more appropriate—this is a point of investigation.

The rationale for it in the second reading is that the pronoun returns to al-Zaqqum, or to the "tree" considering it to be Zaqqum, or considering it as "that which is eaten." It is also said: It refers absolutely to "eating." This is countered by the view that it is far-fetched, because the drinking is upon it (the tree), not upon the act of eating it; furthermore, it involves a dissociation of pronouns. The fact that it might be a common metaphor that does not cause confusion does not negate its being far-fetched. So, reflect upon this.