Tafsir of Sad 38:85

(Allah) said: "The truth is -- and the truth I say that I will fill Hell with you and those of them (mankind) that follow you, together.'' Some of them, including Mujahid, read this as meaning, "I am the Truth and the truth I say.'' According to another report narrated from Mujahid, it means, "The truth is from Me and I speak the truth.'' Others, such as As-Suddi, interpreted it as being an oath sworn by Allah. This Ayah is like the Ayat:

ولكن حق القول منى ﻻمﻼن جهنم من الجنة والناس أجمعين

but the Word from Me took effect, that I will fill Hell with Jinn and mankind together. (32:13) and,

قال اذهب فمن تبعك منهم فٳن جهنم جزآوكم جزاء موفورا

(Allah) said: "Go, and whosoever of them follows you, surely, Hell will be the recompense of you (all) - an ample recompense. (17:63)