The king said to Zadok the priest, “Are you a seer? ¹  Go back to the city in peace! Your son Ahimaaz and Abiathar’s son Jonathan may go with you and Abiathar. ² 

Then Ahimaaz the son of Zadok said, “Let me run and give the king the good news that the Lord has vindicated him before his enemies.” ¹ 

Now Jonathan and Ahimaaz were staying in En Rogel. A female servant would go and inform them, and they would then go and inform King David. It was not advisable for them to be seen going into the city.