What is the ruling on voluntarily fasting the entire month of Rajab, and what is the ruling on singling out this month for fasting on Mondays and Thursdays?

Scholars have differed regarding fasting the entire month of Rajab, between permissibility and detestability. The more cautious approach is not to fast it completely, so as to avoid disagreement. The detestability is removed if one fasts another month with it, or breaks the fast for even one day of it, as stated by Hanbali jurists. Therefore, fasting on Mondays and Thursdays in Rajab is permissible. It is stated in Al-Rawd: "It is detestable to single out Rajab for fasting because it revives a pre-Islamic custom. However, if one breaks the fast during it, or fasts another month with it, the detestability is removed."