And from him, from ‘Uthman, from Sama‘ah, who said:
I asked Him عليه السلام about semen (mani) getting on a garment. Imam عليه السلام said: "Wash the entire garment if the location is unknown to you, whether it is a small amount or a large amount."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 238