Narrated by Ahmad ibn Muhammad, from Safwan, from Al-'Ala', from Muhammad ibn Muslim, from one of the two Imams عليه السلام:
I asked Imam عليه السلام about a man performing ablution - should he wash the inner part of his beard? Imam عليه السلام said: "No."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 382