The hesitation may be in the essence of the intention, or it may be in the description of the intention: 1. If the hesitation is in the essence of the intention: such as intending to fast tomorrow if it is from Ramadan, and not fasting it if it is from Sha'ban, then it is not permissible, and he does not become a faster; due to the lack of certainty which nullifies the pillar of intention, which is the determination with certainty, and the hesitant intention is not a true intention, for the intention is a specification for the action, and hesitation prevents specification. 2. If the hesitation is in the description of the intention: A. The hesitation in the description of the intention between Ramadan and another obligatory fast is disliked as a matter of etiquette, and he is fasting; if it becomes clear that it is from Ramadan, then it is for Ramadan, and if it appears that it is from Sha'ban, then his fast is voluntary; due to the hesitation in the description of the intention, and if he invalidates his fast, he does not have to make it up. B. The hesitation in the description of the intention between Ramadan and a voluntary fast is disliked as a matter of etiquette, and he is fasting; if it becomes clear that it is Ramadan, then it is for it, and if it appears that it is Sha'ban, then his fast is voluntary, and if he invalidates his fast, he does not have to make it up. See: the details of these rulings in "Taqyid al-Haqaiq" 1: 318, and "Al-Hadiyya Al-Alaiyya" pp. 156-157.