I want to ask you about drool (saliva) of swallow (kind of bird)Is it impure ? In south east asia many people mostly non-moslims drink this drool of swallow as medicines. The price of these drool is very expensive. That's why many Muslims in this area make farm of swallow's drool and sell it to non-muslim. What is your opinion, Is it Haram or Halal ?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

We do not know the nature of this bird. It is either one of the birds whose meat is lawful or one of those whose meat is unlawful. If it is among the first category then its saliva is lawful as it is pure according to all scholars of Islam.
Also, if this bird is among the second category, those which meat is unlawful, like the hawk and the falcon then its saliva is also pure. Imam al-Nawawi said: 'When jurists say leftover of the animals they mean what is left after eating or drinking of the animals. And when they say the leftover of the animals is pure or impure they mean their saliva and moistness of their mouths. According to our opinion i.e. al- Shafi'yah the leftover of a cat is pure without any reprehensibility such as the leftover of the other animals like horse, mule, donkey, beast of pry and all other animals whether they are Halal (eatable) or not, their leftover and sweat, are pure except a dog and a pig. This opinion is also reported from Umer bin al-Khatab, Ali, Abu Hurairah, al-Hasan, Atau, al-Dasim and others as narrated in al-Hawi." (al-Majmou).
Therefore, if the commodity is pure, useful, known, and a seller possesses it and can hand over it to the purchaser then selling such a thing is permissible. Therefore, selling the saliva of the bird is permissible if it meets the above conditions.
Allah knows best.