From him, from Ali ibn Al-Sindi, from Uthman ibn Isa, from Sama'ah, from Abu Abdillah عليه السلام, said:
I asked Imam عليه السلام about a man, should he recite aloud in his voluntary (nafl) prayers during the day? Imam عليه السلام said: "Yes."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 312