Ibrahim ibn Hashim from al-Nawfali from al-Sakuni from Imam Ja’far عليه السلام, from his father عليه السلام, from his forefathers, peace be upon them, who said:
Imam al-Sadiq عليه السلام said: “The Prophet صلى الله عليه وعلى آله وسلم, peace be upon him and his family, forbade the speaking of foreign languages (ratanat al-a‘ajim) in the mosques.” (meaning to preserve arabic clarity, reverence, and unity in worship)
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 3, p. 288
