Muhammad bin Sallam (may Allah have mercy on him) said: Amr bin Ma'di Karib fought many battles in the Age of Ignorance (Jahiliyyah); then he lived into the era of Islam and came to the Prophet (peace and blessings be upon him). Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) sent him to Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) at al-Qadisiyyah, and there he showed great valour. Sayyiduna Umar (may Allah be pleased with him) wrote to Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him): I have reinforced you with two thousand men: (namely) Amr bin Ma'di Karib and Talhah bin Khuwaylid, that is, Talhah al-Asadi, (these two are equal to two thousand), so consult them both in matters of war, but do not give them any office.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14169