Question:
How is it to fast on the 15th of Shaʾbān? I’ve heard it is a sunnah (prophetic practice), is that true?
Answer:
Fasting on the 15ht of Shaʾbān is praiseworthy and recommended (mustaḥab).
To single out the fasting on the 15th of Shaʾbān and to deem it as a sunnah (prophetic practice) is not appropriate. However, the 13th, 14th and 15th of every lunar month are considered the bright days (due to the moon being fully apparent). It was the habit of the Prophet Muḥammad (peace and blessing upon him) to fast, monthly, on the bright days. From this perspective, the fasting would be regarded as a sunnah (prophetic practice). (See: Nasaī)
It was also the consistent habit of the Messenger (peace and blessing upon him) to fast the entire month of Shaʿbān except the last two days.
The Prophet (peace and blessings upon him) said, “The best fasts are the fasts of Shaʿbān, in preparation for Ramaḍān.” (Bayhaqī)
And Allāh Knows Best