The ruling on fasting on the day of doubt varies according to intention: 1. Fasting on the day of doubt with a firm intention for Ramadan: It is strongly disliked to fast on the day of doubt if one is certain of their intention for Ramadan, such as saying: "I intend to fast tomorrow for the first of Ramadan this year"; based on the hadith of Ammar (may Allah be pleased with him): "Whoever fasts on the day of doubt has disobeyed Abu al-Qasim," in Sahih al-Bukhari 2: 674 (commentary), and in Al-Mustadrak 1: 585, and in Jami' al-Tirmidhi 3: 70, and he said: "Hasan Sahih." And from Abu Huraira (may Allah be pleased with him), the Messenger of Allah (peace be upon him) said: "Do not precede Ramadan by fasting a day or two, except for a man who was accustomed to fasting, let him fast," in Sahih Muslim 2: 762, and Sahih al-Bukhari 2: 676, and Sahih Ibn Hibban 8: 358, and Al-Musnad Al-Mustakhraj 3: 160. 2. Fasting on the day of doubt with the intention of a voluntary fast: It is permissible to fast on the day of doubt with the intention of a voluntary fast, and it is not disliked. If it turns out to be Ramadan, then it counts as fasting for Ramadan; if it turns out to be Sha'ban, then it counts as fasting for Sha'ban. If he invalidates his fast, he must make it up because he has initiated it with commitment; as Aisha (may Allah be pleased with her) said: "I never saw him fasting in any month more than he fasted in Sha'ban; he used to fast all of Sha'ban, except for a little," in Sahih Muslim 2: 811, and Sahih Ibn Hibban 8: 404. As for what was narrated from Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace be upon him) said: "When half of Sha'ban has passed, do not fast," in Sunan Abu Dawood 2: 300, and Sunan al-Nasa'i 2: 172, and Jami' al-Tirmidhi 3: 115, and he said: "Hasan Sahih," and Abu Zur'ah said: "It is weak," as in the Questions of Al-Baradh'i 1: 388. Ibn Hajar said in Fath al-Bari: "It was narrated by the authors of the Sunan and authenticated by Ibn Hibban and others..." The majority of scholars said that it is permissible to fast voluntarily after the middle of Sha'ban and they weakened the hadith reported about it. Ahmad and Ibn Ma'in said it is weak. 3. Fasting on the day of doubt with an intention other than voluntary: It is disliked to fast on the day of doubt with an intention other than voluntary, such as fasting it as an obligation or a duty. It suffices for what he intended if it turns out to be from Sha'ban, and if it turns out to be from Ramadan, then his intention suffices for Ramadan if he is a resident; because if a traveler intends another obligation, it counts for what he intended; as Abu Huraira (may Allah be pleased with him) said, the Messenger of Allah (peace be upon him) said: "Do not precede Ramadan by fasting a day or two, except for a man who was accustomed to fasting, let him fast," in Sahih Muslim 2: 762, and Sahih al-Bukhari 2: 676, and Sahih Ibn Hibban 8: 358, and Al-Musnad Al-Mustakhraj 3: 160. 4. Fasting on the day of doubt with a hesitant intention: Hesitation may be in the essence of the intention, or it may be in the description of the intention: A. 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 firm resolve. A hesitant intention is not a true intention, as intention is the specification of an action, and hesitation prevents specification. B. If the hesitation is in the description of the intention: - Hesitation in the description of the intention between Ramadan and another obligation is disliked, and he is fasting. If it turns out to be Ramadan, it counts as Ramadan; if it turns out to be 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 make it up. - Hesitation in the description of the intention between Ramadan and a voluntary fast is disliked, and he is fasting. If it turns out to be Ramadan, it counts as Ramadan; if it turns out to be Sha'ban, then his fast is voluntary, and if he invalidates his fast, he does not make it up. For more details on these rulings, refer to Tabyin al-Haqaiq 1: 318, and Al-Hadiyya al-Alaiyya pp. 156-157.