Hushai sent word to King David from Absalom's court via the priests, telling him how to flee Absalom. The priests' sons, Jonathan and Ahimaaz, waited at En-rogel and were sent word by a female servant, so no one could decipher their plan. (2 Samuel 17)
Adonijah's self-exalting coronation
Adonijah sacrificed sheep, oxen, and fattened cattle by the Serpent's Stone, which is beside En-rogel, and he invited all his brothers, the king's sons, and all the royal officials of Judah, but he did not invite Nathan the prophet or Benaiah or the mighty men or Solomon his brother. (1 Kings 1:9-10)