Musnad Abu Ya'la al-Mawsili 115:66

Musa narrated to us, Mu'adh ibn Hisham narrated to us, my father narrated to me, from Qatadah, from Anas, who said: When the Prophet of Allah, Musa, peace be upon him, called his companion to the term that was between them, his companion said to him: "Every ewe that gives birth to [offspring] of a color other than its own, its offspring is yours." He said: So he proceeded and placed ropes upon the water. When they saw the ropes, they were startled and moved about, so they all gave birth to speckled [offspring], except for one ewe. He took their offspring that year.