A.T. Robertson Commentary Hebrews 3:8

"Harden not your hearts, as in the provocation, Like as in the day of the trial in the wilderness," — Hebrews 3:8 (ASV)

Harden not (μη σκληρυνητε). Prohibition with μη and first aorist (ingressive) active subjunctive of σκληρυνω, late verb from σκληρος (dried up, stiff, hard) as in Ac 19:9; Romans 9:18.

As in the provocation (ως ην τω παραπικρασμω). Late compound from παραπικραινω, late verb to embitter (παρα, πικρος), found only in LXX and here and verse 15. It means embitterment, exasperation. For the simple verb πικραινω, to make bitter, see Col 3:19. The reference is to Meribah (Ex. 17:1-7).

Like as in the day (κατα την ημεραν). "According to the day" as in Ac 12:1; 19:23.

Of the temptation (του πειρασμου). The reference is to Massah which took place at Rephidim.