Hazrat Hakam (may Allah have mercy on him) said: "If he says that it is three divorces at once, then a second marriage will be necessary, and if he says them separately, then she will be separated after the first one. This is narrated from Sayyiduna Ali, Abdullah, and Zaid bin Thabit (may Allah be pleased with them)."
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2257
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 1080، وابن أبى شيبة فى «مصنفه» برقم: 18170»