Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: I heard the Noble Prophet (peace and blessings be upon him) say: "Whoever takes an animal for sacrifice and then it gets lost, it is not obligatory upon him to provide a substitute for it; however, if he wishes, he may do so. This is in the case of a voluntary sacrifice. But if it is an animal for a vowed sacrifice, then it is obligatory upon him to provide a substitute."