Sayyiduna Ka'b bin Malik (may Allah be pleased with him) narrates: When twelve men came from al-Aqabah (that is, the Pledge of al-Aqabah), the Prophet (peace and blessings be upon him) ordered them that seventy men should come the following year. So we remained for a year in such a way that one of us would go to his companion with obedience, raml and food, until seventy of us were complete.
Al-Tabarani recorded it; its chain contains a narrator, Ya'qub bin Muhammad al-Zuhri, whom Hajjaj bin al-Sha'ir declared thiqah (trustworthy), while the majority declared him da'if (weak).