I saw the Ansār do something with the Messenger of Allah (may Allah's peace and blessings be upon him) after which I took a pledge upon myself that I would not accompany anyone of them without serving him

Jarīr ibn ‘Abdullāh al-Bajali (may Allah be pleased with him) went out for a journey, in which he used to serve his companions, who were some men of the Ansār. Among them was Anas ibn Mālik, who was younger than Jarīr. It was said to him: "How do you serve them when you are a Companion of the Messenger of Allah (may Allah's peace and blessing be upon him?!"

Jarīr replied: "I saw the Ansār do something with the Messenger of Allah (may Allah's peace and blessings be upon him) after which I took an oath upon myself that I would never accompany anyone of them without serving him." This is a form of honoring those who honor the Prophet (may Allah's peace and blessings be upon him). In fact, honoring and respecting a man's companions is part of honoring and respecting the man himself.

That is why Jarīr regarded that honoring those people is part of honoring the Prophet (may Allah's peace and blessings be upon him).