General Rules

Leather products are impure (najis) and salat 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 halal and was slaughtered according to Islamic laws.
Salat is not permissible in leather products made from skin of predatory animals like lion, leopard, tiger, fox, and jackal.
Similarly, based on obligatory precaution, salat is not permissible in leather products made from non-predatory animals whose meat is forbidden to us like monkeys and elephants even though their hide could be considered tahir if they certainly were (or there is a probability that they were) killed according to Islamic laws.

In all these cases of probability, wearing a belt and things like that made from leather is allowed [in salat], 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 salat in it is not permissible. [With no such probability,] even the use of belt and other things (that cannot conceal the sexual organs in salat) 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%).

The permissibility of the leather of these animals can be achieved by two methods: The first method is that they be slaughtered just as a sheep is slaughtered with all conditions observed.
The second method is that they are hunted by using a gun.
In the latter case, the hunter must be a Muslim; he must invoke Allah’s name while pulling the trigger; he must shoot with the purpose of hunting, and get to the place where the animal fell after it has died or when there was not enough time to slaughter it.

Leather products made in non-Muslim countries from hides of snakes and crocodiles and displayed in non-Muslims markets are considered pure (tahir); and it is permissible to buy, sell, and use them in things that require purity.

Leather products made in Muslim countries and displayed in non-Muslim markets are considered pure (tahir) and it is permissible to use them in salat.

Leather products made in non-Muslim countries whose nature and ritual puritycannot be determined, uncertain whether they are from natural or are permissible to use in salat.

Shoes made from leather of an animal not slaughtered according to Islamic laws do not make the feet najis except through wetness that transfers the impurity.
So, if the foot sweats and the socks become soaked with the sweat, yet the latter does not reach the impure leather, it will not make the feet or the socks impure.

It is permissible to say salat with a leather cap or a leather belt manufactured in non-Muslim countries and bought in non-Muslim markets if there is a probability that these leather products were made from hide of animals that are essentially halal and were slaughtered according to Islamic laws.
This has been mentioned in the third rule of this section.
(See the question-answer section below)

Men are not allowed to wear gold regardless of whether it is a [normal] ring, a wedding ring, a wristwatch, or other things in salat as well as outside it.
It is permissible for them to wear gold-plated items, provided that gold is only considered as a coating and nothing more.

It is not permissible for men to wear what is known as white gold.

Women are allowed to wear gold at all times, even in salat.

Men are not allowed to wear pure and natural silk, neither in salat nor outside salat, except in special circumstances that have been explained in the books of Islamic jurisprudence.

Women are allowed to wear silk at all times even in salat.

Men are allowed to wear ‘doubtful’ silk fabrics and clothes whose origin doubtful, i.e. whether they are made from natural silk or synthetic one. In this case, even salat in them is permissible. (See the question-answer section below)Similarly, it is permissible for them to wear natural silk that has been blended with other material like cotton, wool, nylon, etc.
to the extent that the blended fabric is no longer considered pure silk.
This law also applies, if there is uncertainty about the extent of blending [of pure silk and other material].
In such cases, it is also permissible to say salat in it.

Based on obligatory precaution, men are not allowed to dress up in women’s clothes.

Based on obligatory precaution, Muslims are not allowed to dress up in clothes that are specifically known as the dress of non-Muslims.