612 Benefits and Issues: ➊ From this hadith, the legitimacy of kissing the Black Stone (Hajar al-Aswad) and prostrating upon it is understood. ➋ By prostrating, what is meant is placing the forehead on that spot. Imam Shafi'i rahimahullah, Imam Ahmad rahimahullah, and the majority (jumhur) consider this permissible, although there is some doubt and confusion regarding it. However, Imam Malik rahimahullah has called it an innovation (bid‘ah), and Qadi ‘Iyad has said that this is an isolated (shadh) opinion of Imam Malik rahimahullah. Its details can be seen in Nayl al-Awtar [ج : 5 ، ص : 44].
Source: Bulugh al-Maram: Commentary by Safiur Rahman Mubarakpuri, Page: 612