When David came to the summit, where God was worshiped, Hushai the Archite came to meet him with his coat torn and earth on his head. David said to him, "If you go on with me, you will be a burden to me. But if you return to the city and say to Absalom, 'I will be your servant, O king; as I have been your father's servant in time past, so now I will be your servant,' then you will defeat for me the counsel of Ahithophel. The priests Zadok and Abiathar will be with you there. So whatever you hear from the king's house, tell it to the priests Zadok and Abiathar. Their two sons are with them there, Zadok's son Ahimaaz and Abiathar's son Jonathan; and by them you shall report to me everything you hear." So Hushai, David's friend, came into the city, just as Absalom was entering Jerusalem. (2 Samuel 15:32-37, NRSV)
And it came to pass, that when David was come to the top of the mount, where he worshipped God, behold, Hushai the Archite came to meet him with his coat rent, and earth upon his head: Unto whom David said, If thou passest on with me, then thou shalt be a burden unto me: But if thou return to the city, and say unto Absalom, I will be thy servant, O king; as I have been thy father's servant hitherto, so will I now also be thy servant: then mayest thou for me defeat the counsel of Ahithophel. And hast thou not there with thee Zadok and Abiathar the priests? therefore it shall be, that what thing soever thou shalt hear out of the king's house, thou shalt tell it to Zadok and Abiathar the priests. Behold, they have there with them their two sons, Ahimaaz Zadok's son, and Jonathan Abiathar's son; and by them ye shall send unto me every thing that ye can hear. So Hushai David's friend came into the city, and Absalom came into Jerusalem. (2 Samuel 15:32-37, KJV)
These guys are so loyal to David that they'll sneak in and act as spies and be, effectively, disloyal to Absalom. But that seems pretty fair, given the circumstances.