Does the Hadith: "Every deed of the son of Adam is for him, except fasting, for it is for Me, and I shall reward for it" pertain only to the fasting of Ramadan or does it also include voluntary fasting?

The aforementioned Hadith regarding the virtue of fasting is general, encompassing both obligatory and supererogatory fasts. The word "الصيام" (fasting) with the definite article "أل" (al) indicates generality. Some scholars have pointed out that the Hadith includes every fast, including perpetual voluntary fasting (Sawm al-Dahr), citing the Prophet's (peace be upon him) saying: "Every deed of the son of Adam is for him, except fasting; it is for Me, and I shall reward for it," where he did not specify one type of fast over another.