Al-Hasan (may Allah have mercy on him) said: There is no harm in fasting the three days with gaps between them.
(b) Abu al-Walid said: Narrators other than Hushaym say: "They used to see no harm in fasting this way."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20007