After carefully looking through
Sylloge Numorum Arabicorum Tubingen, Gazna/Kubul, XIV d Hurasan IV, I can't find this coin, which is very unusual.
From the
inscription on the image on the left (the
reverse), I have serious doubts this is a coin of Mas'ud I. Mas'ud I does not have a second line from the bottom like yours. Also the starting character's
style for the third line from the bottom is different than on yours. The
reverse inscription matchs early coins of Mahmud much better. But, then I can't find a match with Mahmud either.
You will need an expert to look at this coin. Or at least someone that can read the
inscription completely.
Howard