Ahmad ibn Muhammad ibn Isa, from Ja‘far ibn Muhammad ibn Abi Zayd, who said:
(Imam) Al-Ridha عليه السلام, peace be upon him, was asked about the tanned skins of foxes. Imam عليه السلام said: "Do not pray in them."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 219