Who do sufis believe is the chief prophet?
ali
fatima
muhammad
abu
bakr

According to Sufis, MUHAMMAD is the chief prophet. 
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Hope this helps :)

Born to Abu Talib and Fatimah bint Asad, ‘Ali was the only person born in the sacred sanctuary of the Ka‘bah in Mecca, the holiest place in Islam, according to many classical Islamic sources, especially Shia ones.[] ‘Ali was the first young male who accepted Islam.[ After migrating to Medina, he married Muhammad's daughter Fatimah. Ali took part in the early caravan raids from Mecca and later in almost all the battles fought by the nascent Muslim community. He was appointed caliph by Muhammad's Companions (Sahaba) in 656, after Caliph Uthman ibn Affan was assassinated ‘Ali's reign saw civil wars and in 661, he was attacked and assassinated by a Kharijite while praying in the Great Mosque of Kufa, dying two days later.