Explanation
Imām an-Nawawī—may Allah have mercy on him—writes in his book Riyāḍ al-Ṣāliḥīn, under the chapter “The Prohibition of Listening to Backbiting,” citing the report of Kaʿb ibn Mālik—may Allah be pleased with him—about his repentance. Kaʿb was one of three men who stayed behind from the expedition of Tabūk without any excuse: Murārah ibn al-Rabīʿ, Hilāl ibn Umayyah, and Kaʿb ibn Mālik. They lagged behind the Messenger of Allah ﷺ with no justification.

When the Prophet ﷺ returned from Tabūk, those who offered excuses came to him, pleading, “By Allah, we were unable,” and they swore to it. The Prophet ﷺ accepted their outward excuses and left their inner reality to Allah.

Kaʿb ibn Mālik and his two companions, however, spoke the truth and said, “We stayed behind with no excuse.” The Prophet ﷺ therefore commanded that they be boycotted, and the Muslims avoided them. If any one of them offered salām, no one returned it. Kaʿb would come and greet the Prophet ﷺ and later say, “I could not tell whether he even moved his lips in reply.”

After forty-eight days the Prophet ﷺ instructed their wives to separate from them. The women went back to their families, except for the wives of Hilāl and Murārah ibn al-Rabīʿ, who remained with their husbands because the men needed their care. As for Kaʿb, his wife returned to her family.

Concerning this remarkable and weighty story, Allah revealed a verse of His Book—a verse that is recited, and for every single letter the reciter earns ten good deeds. What bounty could equal such bounty—that it should be