Abu al-Aliyah (may Allah have mercy on him) narrates from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) that he used to recite: Fasting for three consecutive days.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20008
Humayd bin Qays al-Makki (may Allah have mercy on him) said: I was performing tawaf with Mujahid (may Allah have mercy on him), when a man came and asked: Is it necessary to keep the fasts of expiation consecutively? Humayd (may Allah have mercy on him) said: I said: No. Mujahid (may Allah have mercy on him) struck my chest and said: In the recitation of Ubayy (may Allah be pleased with him) there are the words "mutatabi'at" (consecutive), meaning he should keep them consecutively.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20009
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
Hajjaj (may Allah have mercy on him) said: I asked Ata (may Allah have mercy on him) about the fasts of the expiation of an oath. He said: If he wishes, he may leave gaps. I said: In the recitation of Abdullah (may Allah be pleased with him) there are the words "mutatabi'at" (consecutive). He said: Then we submit to the Book of Allah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20011
Ibrahim said: In our recitation, concerning the expiation of an oath, it has come: fasting for three consecutive days.
(b) Ibn Mas'ud (may Allah be pleased with him) used to recite: Fasting for three consecutive days. All of these are mursal reports from Abdullah bin Mas'ud (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20012