The Holy Prophet (S.A.W.) said: “Islam will continue to be triumphant until there have been twelve Caliphs, all of them from Quraysh.”

Narrated Jabir ibn Samura: The Holy Prophet (S.A.W.) said: “This matter (life) will not end, until it is passed by twelve Caliphs.” He then whispered a sentence. I asked my father what the Prophet said. He said, the Prophet added: “All of them will be from Quraysh.”

Narrated Jabir ibn Samura: I heard the Prophet saying, “There will be twelve commanders (Amir).” He then said a sentence which I did not hear. My father said, the Prophet added, “All of them will be from Quraysh.”

Sahih Muslim (Arabic version) Kitab al-Imaara, 1980 Edition Pub. in Saudi Arabia, v3, p1452-3

Sahih al-Bukhari (English) Hadith: 9.329, Kitabul Ahkam. Sahih al-Bukhari (Arabic) 4:165, Kitabul Ahkam. Hadith #6682 (numbering of al-‘Alamiyyah)

In al-Khisal, Shaykh al-Saduq records the following on pages 466-7:
Ibn Mas`ud’s narration is related in different ways of narration, all related to Mujalid ibn Sa`id. At any rate, in some ways, Mujalid ibn Sa`id is not mentioned.
…Qays ibn `Abd narrated: We were sitting around `Abdullah ibn Mas`ud when a Bedouin came and asked about him. “I am `Abdullah,” answered he. “Did your Prophet (S) tell you about the number of his successors?” asked the Bedouin. “Yes, he did. They are twelve, like the number of the Israelite disciples,” answered `Abdullah.

In the same documentation, the narrations are recorded in Kamal al-Din wa Itmam al-Ni`mah, 271.

The famous scholar al-Dhahabi says in Tadhkirat al-Huffaz, vol. 4, p. 298, and Ibn Hajar al-’Asqalani says in al-Durar al-Kaminah, vol. 1, p. 67 that Sadruddin Ibrahim bin Muhammad bin al-Hamawayh al-Juwayni al-Shafi’i was a great scholar of Hadith.
The same Al-Juwayni reports from Abdullah ibn Abbas (r) from the Prophet (s) who said, “I am the chief of the Prophets and Ali ibn Abi Talib is the chief of successors, and after me my successors shall be twelve, the first of them being Ali ibn Abi Talib and the last of them being Al-Mahdi.”

Al-Juwayni also narrates that the Messenger of Allah (s) informed: “I and Ali and Hasan and Husayn and nine of the descendants of Husayn are the purified ones and the inerrant.” [Al-Juwayni, Fara’id al-Simtayn, Mu’assassat al-Mahmudi li-Taba’ah, Beirut 1978, p. 160.]