Abu Dawud Book 13, Hadith Number 3066.

Narated By Abdullah ibn Umar : The Prophet (PBUH) gave az-Zubayr the land as a fief up to the reach of his horse when he runs. He, therefore, made his horse run until it stopped. He then threw his flog. Thereupon he said: Give him (the land) up to the point where his flog has reached.