Ahmad ibn Muhammad, from al-Walid ibn Aban, who said:
I said to (Imam) Al-Ridha عليه السلام, peace be upon him: "May I pray in the fur of the fennec and the squirrel?" Imam عليه السلام said: "Yes." So I asked: "Is it permissible to pray in fox skins if they are from a properly slaughtered animal (dhakiyyah)?" Imam عليه السلام said: "Do not pray in them."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 220