If one observes Sawm (Fast) or breaks Sawm on the thirtieth day of Sha‘ban without sighting the new moon, would their Sawm be valid?
Please support your answer with evidence.
It is not permissible for a Muslim to fast on the thirtieth of Sha‘ban if sighting the new moon has not been confirmed on the eve of that day. An exception to the prohibition of Sawm on the thirtieth of Sha‘ban is made if it coincides with a day that someone habitually fasts, such as Sawm on Monday or Thursday. Accordingly, a person who has this habit is permitted to fast this day along with other previous days of Sha‘ban, because the Prophet (peace be upon him) said:
Do not observe Sawm for a day or two days ahead of Ramadan, except a person who is in the habit of observing a particular Sawm; they may fast on that day.
(Part No. 10; Page No. 93)