Tafsir of Ash-Shu`ara' 26:97

"By Allah, we were indeed in clear error."

The in (إن) is a lightened form of the heavy (emphatic) inna (إنَّ). Its subject, according to what has been said, is the pronoun of state (ḍamīr al-sha’n) which is omitted, and the lam (اللام) serves as a separator between it and the negative particle, as held by the Basrans. That is: "It is—meaning the state of affairs—that we were in clear error."

The Kufans held that in is negative, and the lam bears the meaning of illa (except), that is: "We were not but in an obvious error in which there is no concealment." Their description of it as "obvious" is for the sake of hyperbole in manifesting their remorse and deep regret, and in clarifying the error of their judgment despite the clarity of the truth. This is indicated by their commencing the statement with the letter ta (تاء), which signals astonishment, according to what has been said.