Which one of the following actions may be regarded as Mubāℎ?

Acquisition of knowledge is considered Mubāℎ in Islam. Mubāℎ means permissible or allowed in Islam. Islam encourages seeking knowledge and considers it as an important act of worship. It is the duty of every Muslim, both men and women, to seek knowledge throughout their lives. Smoking, on the other hand, is considered Ḥarām (forbidden) in Islam because it harms the body, which is considered a trust from God. Salāt ash-Shaf, which is an additional prayer that can be performed after the obligatory prayers, is also Mubāℎ in Islam. Shaking hands while greeting is also Mubāℎ in Islam. It is a common practice among Muslims and is considered a polite and respectful way of greeting each other. In summary, acquiring knowledge, shaking hands while greeting, and Salāt ash-Shaf are all permissible and considered Mubāℎ in Islam, while smoking is considered Ḥarām.