«صوم ثلاثة أيام من كل شهر ورمضان إلى رمضان صوم الدهر وإفطاره»
The Prophet (peace and blessings be upon him) said:
"Fasting three days of every month, and fasting from one Ramadan to the next Ramadan, is equal to fasting perpetually and breaking the fast (in between)."
Hadith Referenceصحیح الجامع الصغیر / حرف الصاد / 3802