Luke 1:20

Thou shalt be silent (esh siwpwn). Volitive future periphrastic. Not able to speak (mh dunameno lalhsai). Negative repetition of the same statement. His dumbness will continue "until" (acri h hmera) the events come to pass "because" (anq wn). The words were to become reality in due season (kairon, not crono, time).