Firstly: Defining the Freeing of Slaves
Riqab linguistically: is the plural of raqabah, the neck. It then became a metaphor for the whole human being, using a part of a thing to name the whole, as is an Arabic linguistic style. A "freed neck" is the same as a freed slave, male or female.
Fi al-riqab, literally "for the necks," actually means fi fakk al-riqab, for the freeing of the necks, and this refers to the self-freed slave (mukatab)  The self-freed slaves are those who bought themselves from their masters, and their name mukatab is taken from kitabah, writing. This is so because the contract is written between the master and his slave. who does not own what he contractually agreed to free himself. It also includes slaves freed by the ruler and their allegiance is to the Muslims.
Secondly: Charity for Freeing Slaves
It is permissible to give charity to the self-freed slave. This is the position of the majority: Hanafis, Shafi`is, Hanbalis, a narration from Malik, the position of Ibn Hazm, and the view held by the majority of scholars.
Thirdly: Paying Charity to Buy a Slave to Free Him
It is permissible to use charity to buy a slave in order to free him. This is the position of the Malikis, and Hanbalis. It is also the chosen position of Abu `Ubayd al-Qasim ibn Sallam, Ibn al-Mundhir, Ibn Hazm, Ibn Taymiyyah, al-Shawkani, Ibn Baz, Ibn `Uthaymin, and many scholars.
Fourthly: Muslim War Prisoners
The share of freeing slaves also encompasses the ransoming of Muslim war prisoners. This is the position of Ahmad, Ibn Habib from the Malikis, chosen by Ibn Taymiyyah, Ibn Baz, Ibn `Uthaymin, and the decision of the Islamic Fiqh Academy as part of the Organisation of Islamic Cooperation.