Musannaf Ibn Abi Shayba 7:301

Marwan ibn Mu'awiyah narrated to us, from Marwan ibn Mahan al-Taymi, who said: I heard al-Sha'bi—and he was asked about a woman who vowed to slaughter a cow: "Is it permissible for her to sell its hide?" He said: "Yes." Ibn Ashwa' said: "But I do not know that." Al-Sha'bi said: "If you had said its meat, there would be no harm in it. She only vowed its blood, and she has already shed its blood."