Asim bin Kulayb narrates from his father, and he from a man of the tribe of Muzaynah or Juhaynah, that the Companions of the Messenger of Allah (peace and blessings be upon him), a day or two before the sacrifice, used to give two jadh'ahs (six-month-old lambs) and take one thani (two-year-old animal) (in exchange for the larger animal). So the Messenger of Allah (peace and blessings be upon him) said: "Indeed, the jadh'ah suffices for what the thani suffices for." This is a hadith in which there is disagreement over Asim bin Kulayb, and it is among those that the two Shaykhs did not record. However, I have made it my condition to use it as evidence, and in my view this hadith is sahih (authentic), because all agree on mentioning the Companion in it, and then the Imam of the discipline of hadith, Sufyan al-Thawri, also named him explicitly.