Tafsir of Al-Hijr 15:78

(And indeed, the companions of the thicket were wrongdoers.)

They are the people of Shu'ayb, upon him be peace. Al-Ayka (the thicket) in its origin refers to intertwined trees; the singular is aykah. The poet said:

She reveals, with the primary feathers of a wood-dove, White teeth whose gums were darkened with antimony.

The intended meaning is a ghaydah—that is, a spot dense with trees—based on what has been narrated: that these people used to reside in this ghaydah, the most common of its trees being the dawm (doum palm), though it is also said they were lote trees. Allah, the Exalted, sent Shu'ayb to them, but they belied him, so they were destroyed as you will hear, if Allah the Exalted wills.

It is also said: It is a town they inhabited, and its application to what has been mentioned is either by way of metaphorical transfer or by naming the place after what dwells within it. It then became dominant until it turned into a proper noun. The claim that it is a proper noun is supported by the fact that it was recited in Surat al-Shu'ara' as "Lykah," which is diptote (non-declinable).

According to the Basrans, Inna (in "Wa-in") is the lightened form of the heavy Inna; its pronoun of state (dameer al-sha'n) is omitted, and the lam is the separator (al-fariqah). According to al-Farra', it is the negative particle, having no subject, and the lam carries the meaning of illa (except). The reliable interpretation is the former; meaning: and the state of affairs was that those people were those who transgressed the limit.