Abu Dawud

Benefits and Issues:
➊ The meaning of joining Sha'ban with Ramadan is that one observes fasts in Sha'ban until Ramadan begins.

➋ The wisdom of the Shari'ah appears to be that there should be a distinction between worship and habit. Therefore, if someone has the habit of observing the Sunnah fasts on Mondays and Thursdays, or happens to have made a vow (nazr), or has a missed (qada) fast remaining, then there is concession for him to fast a day or two before Ramadan begins.

English Commentary:
1:
The wisdom behind this prohibition is that obligatory fasts should not become mixed up with voluntary fasts, and so that some people do not mistakenly consider them to be obligatory. Therefore, for the preservation of boundaries, the Prophet sallallahu alayhi wa sallam forbade fasting from both sides, because in previous nations such kinds of alterations and changes used to occur, which opened the way to excessiveness in religion. For this reason, it was prohibited.

2:
For example, if one already has the habit of fasting on Thursdays, Mondays, or the white days (Ayyam al-Beed), and this day happens to coincide with one or two days before Ramadan, then one may fast, as this is not considered as anticipating Ramadan.

(1) The nature of the disagreement among them is that, among the students of Shu’bah below Abu Hurairah radi Allahu anhu in the chain of narrators, there is a difference. When Isma’il ibn ‘Ulayyah narrates from Imam Shu’bah, he transmits the words "fa’uddu thalathin" (count thirty). However, when Waraqah ibn ‘Umar al-Yashkuri narrates from him, he says "faqdurū thalathīn" (estimate thirty). But this does not affect the authenticity of the hadith in any way. For further details and research, see (Fath al-Bari: 4/21, Hadith number: 1909).

(2) Whatever the month may be, the ruling is the same. In some narrations, the word Sha’ban appears only because the fasts are related to the end of Sha’ban; otherwise, even Ramadan itself, in this situation (i.e., when the crescent of Shawwal is not sighted), will be counted as thirty days.

This instruction is for the last days of Sha'ban so that voluntary fasts do not become connected to the obligatory fasts, maintaining a distinction and highlighting the importance of Ramadan al-Mubarak. Furthermore, it ensures that a fast is not observed on a doubtful day (the 30th of Sha'ban). The case of “someone who habitually fasts on a specific day” falling on a prohibited day is as follows: for example, if a person habitually fasts every Monday, and the last Monday of Sha'ban falls on a day that is doubtful—whether it is the 30th of Sha'ban or the 1st of Ramadan—then he may fast on that day according to his previous habit.

Benefits and Issues:
➊ One form of fasting a day before Ramadan is the fast of doubt (sawm al-shakk). Its details were explained in the previous chapter, that is, on a day when, due to cloudiness or some other reason, the legal testimony for sighting the crescent could not be established, and people are in doubt whether it is the 30th of Sha'ban or the 1st of Ramadan. To fast on that day with the intention that if it is later established that Ramadan had begun, then this will count as a Ramadan fast, otherwise it will be considered a voluntary (nafl) fast—this form is not permissible.

➋ The second form of fasting before Ramadan is to fast despite having certain knowledge that Ramadan has not begun. In this way, to combine voluntary (nafl) and obligatory (fard) acts is also not permissible; rather, this act outwardly resembles adding to obligatory worship.

➌ The third form of fasting before Ramadan is, for example, a person habitually fasts on Mondays and Thursdays according to the Sunnah. Coincidentally, the 29th or 30th of Sha'ban falls on a Monday or Thursday, and the next day becomes the 1st of Ramadan. Thus, this fast is adjacent to Ramadan. Or someone had obligatory (qada) fasts to make up, which ended on the 29th or 30th of Sha'ban. In these cases, or in any similar situation, the intention was not to combine these fasts with those of Ramadan, but coincidentally these fasts happened to be adjacent to the fasts of Ramadan. In this case, it is permissible and there is no harm in it.