Qanbar (RA) loved Imam Ali (AS) a lot and tried to look after him.

One night Imam Ali (AS) noticed that Qanbar (RA) was moving behind him, and Imam (AS) asked: What has happened that at this time of night you are following me? Qanbar (RA) replied: I have come to look after you. Imam Ali (AS) said: Do you protect me from the residents of the sky or the earth? Qanbar (RA) replied: From the residents of the earth. Imam Ali (AS) added: The residents of the earth cannot harm me except by God’s permission; go back, and Qanbar (RA) returned on Imam’s (AS) command [1].

[1] Osul Kafi, Vol. 2, Page 59.

Source: en.shafaqna.com