What is the reason for the prohibition of drinking from the mouth of a waterskin?

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The questioner : May Allah reward you with good, O Shaykh. Well... regarding drinking from the mouth of a waterskin.

The Shaykh : Do you know what a waterskin is?

The questioner : ... You mean.

The Shaykh : Yes, I mean that.

The questioner: Yes.

The Shaykh : A waterskin is not open; if there is an insect in it, when a person comes to drink from it, an insect may come out with the water and enter his stomach, causing him harm.

The questioner: Yes.

The Shaykh : Therefore, if one pours from the waterskin into an open vessel, one is safe from anything...

The questioner : ...

The Shaykh : This is one thing, and there is another thing: since the waterskin is made of leather, if one drinks from the mouth...

The questioner: Yes.

The Shaykh : From the mouth of the waterskin, the bad breath from the mouth clings to the leather and attaches to it, so it becomes a source of impurity.

The questioner: Yes.

The Shaykh : For these reasons, the Lawgiver prohibited it.

The questioner : May Allah reward you with good, O Shaykh.

The Shaykh : May Allah preserve you.

The questioner: Peace be upon you.

The Shaykh : And upon you be peace, and the mercy of Allah and His blessings.

The Shaykh : Did you finish, or did you not finish?

The questioner : Not yet.