From Sahih Muslim (Hadith 3674):
Abu Sahba' said toIbn 'Abbas (Allah be pleased with them):Do you know that three (divorces) were treated as one during the lifetime of Allah's Apostle (ﷺ), and that of Abu Bakr, and during three (years) of the caliphate of Umar (Allah be pleased with him)? Ibn Abbas (Allah be pleased with them) said: Yes
Reference: Muslim 3674