Sahih Bukhari Volume 9, Book 89, Hadith Number 331.

Narrated By ‘Abdullah bin Ka’b bin Malik : Who was Ka’b’s guide from among his sons when Ka’b became blind: I heard Ka’b bin Malik saying, “When some people remained behind and did not join Allah’s Apostle in the battle of Tabuk…” and then he described the whole narration and said, “Allah’s Apostle forbade the Muslims to speak to us, and so we (I and my companions) stayed fifty nights in that state, and then Allah’s Apostle announced Allah’s acceptance of our repentance.”