Musnad Ahmad 27:1998

Hammad ibn Khalid al-Khayyat narrated to us, from Abdullah—meaning al-Umari—from Nafi, from Ibn Umar: That the Prophet, peace and blessings of Allah be upon him, granted al-Zubayr a piece of land [the size of] the reach of his horse, in a land called Thareer. He made the horse run until it stopped, then he threw his whip and said: "Give him [land] up to where the whip reached."