What justification does the Ahmadiyya movement have that Prophet Muhammad wasn't the last prophet?

The Ahmadiyya movement believes that Muhammad is not the final prophet in the definitive sense but rather the last of the law-bearing prophets. They claim that the concept of finality of prophethood does not exclude the possibility of non-law-bearing prophets arising after him. This perspective relies on their interpretation of certain Qur'anic verses and hadith.

One of the key verses they reference is from Surah Al-Ahzaab, which states: Muhammad is not the father of any man among you, but he is the messenger of Allah and the Seal of the Prophets; and Allah is ever Aware of all things. 33:40. The Ahmadis interpret "Seal of the Prophets" to mean that Muhammad completed the prophetic tradition, but they argue that this does not preclude the coming of future prophets who do not bring new laws, but rather confirm and revive the teachings of Muhammad.

Moreover, the Ahmadis cite the hadiths that discuss the coming of a Messiah or a Mahdi in the latter days but interpret these figures as not being new prophets in the traditional sense. They believe that Mirza Ghulam Ahmad, the founder of the Ahmadiyya movement, fulfills this role as the Promised Messiah and Mahdi, thus continuing the prophetic mission without contradicting the finality of prophethood.

In summary, the Ahmadiyya movement justifies its belief in the continuation of prophecy through a re-interpretation of the concept of finality and the role of Mirza Ghulam Ahmad as a non-law-bearing prophet. This view is not accepted by mainstream Sunni and Shia Islam, who hold firmly that Muhammad is indeed the last prophet with no possibility of further prophecy.