It has been narrated in 271 traditions of the Holy Prophet (saw) that , "Islam will not be completed till such time that I am followed by twelve successors, all of whom will be from Quraysh"

(Quraysh is the tribe of the Holy Prophet. (saw). By limiting the arrival of the successors to Quraysh, the Holy Prophet has indicated that his successors will be Arabs, not Persians or individuals from any other lineage.)

For the benefit of my readers, a few references for this narration are given below:
1. Sahih Bukhari, volume 4, page 175, ed. Egypt, 1355 AH
2. Sahih Tirmidhi, volume 2, page 45, ed. Delhi, 1342 AH
3. Sahih Muslim, volume 2 page 191, ed. Egypt, 1348 AH
4. Sahih Abi Dawood, volume 2, Kitab Al Mahdi, page 208, ed. Egypt
5. Tarikhe Baghdadi, volume 2, page 126, 1349 AH
6. Musnade' Ahmed Ibne' Hambal
    - Ibid, volume 5, page 106, 34 narrations
    - Ibid, volume 5, page 76, 1 narration
    - Ibid, volume 5, page 78, 2 narrations
    - Ibid, volume 5, page 79, 1 narration
    - Ibid, volume 5, page 90, 3 narrations
    - Ibid, volume 5, page 92, 2 narrations
    - Ibid, volume 5, page 93, 3 narrations
    - Ibid, volume 5, page 94, 1 narration
    - Ibid, volume 5, page 95, 1 narration
    - Ibid, volume 5, page 96, 2 narrations
    - Ibid, volume 5, page 97, 1 narration
    - Ibid, volume 5, page 98, 4 narrations
    - Ibid, volume 5, page 99, 3 narrations
    - Ibid, volume 5, page 100, 1 narration
    - Ibid, volume 5, page 101, 2 narrations
    - Ibid, volume 5, page 107, 2 narrations
    - Ibid, volume 5, page 108, 1 narration
    - Totally, 65 narrations
7. Mustadrak Alas Sahihayn, volume 3, page 617, ed. Hyd, 1336 AH
8. Ibid, volume 3, page 618, ed. Hyderabad, 1336 AH
9. Tayseeral Wusool Ila Jame'al Usool, vol 2, pg 34, ed. Egypt, 1346 AH
10. Tarikhal Khulafa, page 8, ed. India
11. Yanabiul Mawaddah, page 665
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Interestingly, Mirza Ali Mohammed Shirazi, the Bab himself testifies to the twelve Imams (successors of the prophet) and actually lists them in sequence in his book Sahifae Adaliyah.

Given that the number of the Holy Imams (as) is twelve - testified by Mirza Ali Mohammed Bab himself along with their names, then where is the question of the Bab being accepted as the Mahdi (the Twelfth Imam)? Perhaps the Bahais can answer this question.

The Bahais have usurped not just the position of the 12th Imam, but also the titles which are attributed to him. Refer to the books of Tafseere' Kauthar, Dalelus Sabah and Sahifae Adaliyah of the Bab. In each book, the Bab takes the name of the Twelfth Imam and his titles. Bahais have wrongfully attributed these titles to the Bab and Bahaullah.