A Code of Practice For Muslims in the West:
Dress & clothings» General Rules
Ayatullah al Uzama Syed Ali al-Husaini Seestani
Wearing if leather belts / watches / bands in Salaat
195. Leather products are impure (najis) and salãt in them is not permissible, if we know that they have been made from the hide of an animal not slaughtered according to Islamic laws. Such products are considered pure and salat in them is permissible, if there is a probability that they were made from skin of an animal that is essentially halãl and was slaughtered according to Islamic laws.
In all these cases of probability, wearing a belt and things like that made from leather is allowed [in salãt], provided that they are not big enough as to conceal the private parts. If there exists no probability that it was slaughtered according to Islamic laws, and, on the contrary, we are sure that it comes from skin of an animal that was not slaughtered according to Islamic laws, then it is najis and salãt in it is not permissible. [With no such probability,] even the use of belt and other things (that cannot conceal the sexual organs in salãt) is not permissible on the basis of obligatory precaution. It would be the same law if the probability was very low that sensible people ignore it (for example, 2%).
'O God, carry us in the ships of Thy deliverance, give us to enjoy the pleasure of whispered prayer to Thee, make us drink at the pools of Thy love, let us taste the sweetness of Thy affection and nearness, allow us to struggle in Thee, preoccupy us with obeying Thee, and purify our intentions in devoting works to Thee, for we exist through Thee and belong to Thee, and we have no one to mediate with Thee but Thee!' Imam Sajjad ('A); Sahifa al-Sajjadiyya