Fasting in the Month of Shaʿbān Is from the Sunnah
A questioner asks the noble scholar, Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn (raḥimahullāh), about her mother's forbiddance of her fasting Mondays and Thursdays in the month of Shaʿbān due to it allegedly not being from the Sunnah to do so. The esteemed scholar corrects this misnomer and adds scholarly commentary upon the matter.
Fasting in Shaʿbān is from the sunnah and an individual should fast all but a little of it [i.e. the majority of it].
Shaykh Muḥammad ibn Sāliḥ al-‘Uthaymīn (رحمه الله).
A questioner mentions to Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn (رحمه الله) that she fasts every Monday and Thursday and also in the month of Shaʿbān; however, her mother prevents her from fasting in Shaʿbān claiming that it is not permitted to fast before Ramaḍān.
The shaykh (رحمه الله) responded:1
Fasting [on a Monday and Thursday] is recommended, for verily, the Prophet (ﷺ) would fast on Mondays and Thursdays, and he (ﷺ) would say: 'They are the days in which deeds are presented to Allāh, and I like my deeds to be presented [to Him] when I am fasting.'2 It is also recommended to increase [one's] fasting in Shaʿbān, for verily the Prophet (ﷺ) would not fast a month the way in which he would fast Ramadān except Shaʿbān.3 Therefore, he (ﷺ) would fast the majority of it. However, whoever never fasted in Shaʿbān, then it is forbidden for him to do so, meaning, it is forbidden for him to fast a day or two before Ramaḍān4 due to the statement of the Prophet (ﷺ): 'None of you should fast a day or two before Ramaḍān, unless he has the habit of fasting [supererogatory fasts and his fasting coincides with that day] then he can fast it.'
Therefore, it is important to inform your mother that fasting in Shaʿbān is from the sunnah and an individual should fast all but a little of it [i.e. the majority of it].
 Source: حكم صوم أيام من شعبان
 Reported by Aḥmad, Abū Dawūd, al-Nasāʾī and others. Shaykh al-Albānī deemed it to be authentic.
 Despite the fact that this statement alludes to the fact that the Prophet (ﷺ) would fast Shaʿbān in its entirety and that this is supported by what al-Bukhārī, Muslim and others have narrated on the authority of ʿĀʾishah, that she said: "The Prophet (ﷺ) did not observe voluntary fasting so frequently during any other month as he did during Shaʿbān. He observed fasting throughout the month of Shaʿbān." They also reported that she said: "He (ﷺ) observed fasting during the entire month of Shaʿbān, except a few days." What is most correct is that the Prophet (ﷺ) never fasted an entire month except Ramaḍān. Al-Bukhārī, Muslim and others have narrated on the authority of ʿĀʾishah that she said: “I never saw Allah's Messenger (ﷺ) fasting for an entire month, except the month of Ramaḍān, and I did not see him fasting in any month more than in the month of Shaʿbān." As for what was intended when she said that he observed fasting throughout the month of Shaʿbān, then the answer is that he fasted the majority of its days, so much so it is as if he fasted all of it. This is why the shaykh himself said: "Therefore, he (ﷺ) would fast the majority of it." Therefore, with this understanding the Āḥadīth do not contradict each other, and Allah knows best.
 What is intended here is, whoever did not fast the former part of Shaʿbān, it is not permitted for him to fast the latter part of it, because of the Ḥadīth mentioned above, and also, because of his (ﷺ) statement: "When Shaʿbān is at its middle, do not fast." Therefore, if you did not fast in the first half of Shaʿbān, do not begin fasting in the second half of it, except if you had outstanding fast to make up from the previous Ramaḍān.
Translated by: Musa Shaleem Mohammed