Sheikh Muhammad al-Khudayrî
This subject has been thoroughly discussed by Ibn Taymiyah in the introduction of volume thirty three of his book Majmû` al-Fatâwa.
It was also discussed by Ibn al-Qayyim in Ighâthah al-Lahfân min Masâ’d al-Shaytân, in which he says: “It is preferred for the person who wishes to divorce to abide by the commands of Allah and His Messenger.” He then goes on for the next 45 pages discussing this question in the most painstaking detail. He ultimately arrives at the same conclusion as his teacher Ibn Taymiyah. He says: “Three pronouncements of divorce offered during one period of purity between two menstrual cycles count as a single divorce.”
Ibn `Abbâs relates to us the way divorce used to take place at the time of the Companions. He said: “Divorce at the time of the Prophet (peace be upon him), then during Abû Bakr's reign, and first two years of `Umar’s reign was by counting the three pronouncements of divorce as a single divorce. Then `Umar said: ‘People are hastening something in which they have been granted time, so we should put a check to this.' Then he decided to consider the three pronouncements given at once as three divorces.”
`Umar’s ruling is the opinion adopted by the four schools of thought. [Refer to: al-Mabsût (6/57), al-Muhadhdhab (2/107), and al-Mughnî (8/243)]
There are two opinions on this matter. In consideration of the evidence and the practice at the time of the Prophet (peace be upon him), the strongest opinion is that three pronouncements of divorce given on one occasion count as a single divorce.
And Allah knows best.
Source: Islam Today