Tawus (may Allah have mercy on him) narrates that a man named Abu al-Sahba' used to ask Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) a great many questions. He said: Do you not know that when a man divorced his wife three times before consummation, it was counted as only one in the time of the Messenger of Allah (peace and blessings be upon him), of Sayyiduna Abu Bakr, and at the beginning of the caliphate of Sayyiduna Umar (may Allah be pleased with them both)? Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "Of course! When a man divorced his wife three times before consummation, it was counted as only one in the time of the Prophet (peace and blessings be upon him), of Sayyiduna Abu Bakr, and in the early period of the caliphate of Sayyiduna Umar (may Allah be pleased with them both). Then when Sayyiduna Umar (may Allah be pleased with him) saw that people had begun giving divorces in succession (tatra), he enforced all three."
The Shaykh (may Allah have mercy on him) said: (This is) when he intends to give the three divorces in succession.
(b) Imam al-Sha'bi (may Allah have mercy on him) narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) concerning a man who divorced his wife three times before consummation that he said: "It was a knot in his hand which he released all at once; but if they were in succession, then it is nothing."
Imam Sufyan al-Thawri (may Allah have mercy on him) said: "Tatra" means: "You are divorced, you are divorced, you are divorced"; she becomes separated by the first one alone, and the other two are nothing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14985