Ibn Abi Najih (may Allah have mercy on him) narrates from Ata or Tawus (may Allah have mercy on them both): If he wishes, he need not keep the three days' fasts consecutively. Mujahid (may Allah have mercy on him) said: In the recitation of Abdullah (may Allah be pleased with him) there are the words "mutatabi'ah", that is, "consecutive." He said: Then they are consecutive.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20010