A.T. Robertson Commentary Hebrews 3:15

"while it is said, To-day if ye shall hear his voice, Harden not your hearts, as in the provocation." — Hebrews 3:15 (ASV)

While it is said (εν τω λεγεσθα). Locative case with εν of the articular present passive infinitive of λεγω, "in the being said." Thus the author (cf. same phrase in Ps 42:4) introduces the repeated quotation from verses 7,8. Probably it is to be connected with κατασχωμεν, though it can be joined with παρακαλειτε in verse 13 (treating 14 as a parenthesis).