According to the version reported by Ibn Isḥāq, the Prophet ﷺ paired Kaʿb with Ṭalḥa in the bond of brotherhood.
Kaʿb once recited to ʿAlī some lines he had composed about ʿUthmān:
“He stayed his hands and then shut his door,
convinced that Allah is never unaware.
He said to those within his house, ‘Do not fight—
may Allah pardon everyone who keeps out of battle.’
So tell me, did you not see how Allah poured upon them
enmity and hatred after they had been joined in affection?
And did you not see how goodness turned its back on them,
fleeing like a startled flock of ostriches?”
ʿAlī replied, “ʿUthmān kept privileges for himself and misused that favoritism, while you lost your composure and behaved poorly in your agitation (1).”
Al-Zuhrī narrated from ʿAbd al-Raḥmān ibn ʿAbd Allāh ibn Kaʿb, from his father:
“I heard Kaʿb say, ‘I never stayed behind from any expedition of the Messenger of Allah ﷺ until the campaign of Tabūk—except Badr. Nor would I like to have been present at Badr if that meant I missed my pledge on the Night of al-ʿAqaba (2). Seldom did the Messenger…’”
‘Urwa narrates from his father, from al-Zubayr ibn al-‘Awwam: “Allah revealed concerning us—the clans of Quraysh and the Ansar—the verse: ‘wa-ulu-l-arham ba‘duhum awla bi-ba‘d fi kitab Allah’ (Those who are bound by kinship are nearer to one another in the Book of Allah). When we people of Quraysh came to Madinah, we arrived with no property. We found the Ansar to be excellent brothers; we concluded bonds of brotherhood with them and even inherited from one another … Among the things I said was: ‘By Allah, my sons, had he died that day no one but I would have inherited him—until Allah sent down this verse about us, the Quraysh and the Ansar—whereupon we reverted to the normal rules of inheritance.’” Its chain of transmission is hasan (sound).
Ibn ‘Asakir records in his Ta’rikh (14/288/2) through the route of Abu-l-Qasim al-Baghawi—‘Abd al-A‘la al-Narsi—Hammad ibn Salama—Hisham ibn ‘Urwa—from his father: “The Messenger of Allah ﷺ established a pact of brotherhood between al-Zubayr ibn al-‘Awwam and Ka‘b ibn Malik. Ka‘b was severely wounded at Uhud, so al-Zubayr led his mount by its halter while supporting him. Had Ka‘b died that day, al-Zubayr would have inherited him. Then Allah revealed: ‘wa-ulu-l-arham ba‘duhum awla bi-ba‘d fi kitab Allah.’”
(1) See al-Aghani 6/233–234.
(2) Al-Bukhari and Muslim also relate: “I was present with the Messenger of Allah ﷺ at the pledge of al-‘Aqabah, when we mutually pledged ourselves to Islam; I would not trade that scene for having been at Badr, even though Badr is better-known among the people.”