Do not kill game while you are on pilgrimage...

Do not kill game while you are on pilgrimage, and whoever among you kills it intentionally, the compensation (for it) is the like of what he kills, from the cattle, as two just persons among you shall judge, as an offering to be brought to the Ka’ba or the expiation (of it) is the feeding of the poor or the equivalent of it in fasting so that he may taste the unwholesome result of his deed' (Holy Qur'an, Surah Maida 5:95)." Then the Imam (as) turned to al-Zuhri and asked him, "Do you know how its equivalent is met by fasting, O Zuhri?" The latter said, "No, indeed, I do not know." Imam Zaynul-’Abidin (as) then said, "The game is first to be estimated, then the estimated value is to be measured by its equivalent in charity, then such a measure is to be weighed, so he should fast one day for each half a measure unit.

And the covenant ( nathr ) fast is obligatory, and so is the fast of I’tikaf . As regarding the prohibited fast, it is forbidden to fast on Eid al-Fitr, Eid al-Adha, the three days of tashreeq [^1], and the fast of doubt: Allah ordered us to fast it with the month of Sha’ban and anyone among us is prohibited from singling himself out to fast when everyone else is not sure whether it is the inception of the month of Ramadhan or not." I said to him, "May I be sacrificed for you, but if he did not fast during the month of Sha’ban, what should he do?" The Imam (as) said, "He should make the intention on the uncertain night that he is fasting the month of Sha’ban; so, if it turns out to be the month of Ramadhan, he will receive his reward, but if it becomes evident that it was, indeed, the month of Sha’ban, he will not have committed any harm." I then asked him, "How can voluntary fast make up for a compulsory one?" He (as) said, "If someone voluntarily fasts one day during the month of Ramadhan without knowing that it is the month of Ramadhan, then he finds out that it was, should he fast again?!

The obligation is regarding the day itself. The wisal fast[^2] is prohibitive, and to fast each day of your life is likewise prohibitive. "As regarding optional fast, it is to fast on Fridays, Thursdays, and Mondays, the white ( beed ) days [^3], the fast of six days during the month of Shawwal following the month of Ramadhan, the fast on the standing day at Arafat, and the day of Ashura; all these occasions are optional; one may or may not fast during them.