We believe that every thing which was stated , said , practice or approved by the Prophet Muhammad (SAWA) is from Allah ( SWT) and we Must follow it as Allah (SWT) has ordered us in Quran ( Whatever is brought to you by The Messenger, you must take it, and whatever he tells you to leave, you must leave it) Sura 59, Verse 7.
The Prophet Muhammad (SAWA) has very clearly said the : My successors will be twelve, all of them from Quraish.
This Hadeeth is narrated in
1. Saheeh Al-Bukhari , Hadeeth number 6682 .
2. Saheeh Muslim, Hadeeth number 3393 and 3394 and 3395 and 3396.
3. Musnad Ahmad Ibn Hanbal , Hadeeth number 3593 and 3665 and 19875 and 19884 and 19887 and 19892 and 19901 and 19914 and 19920 and 19922 and 19925 and 19944 and 19946 and 19956 and 19963 and many other narrations in this meaning.
4. Sunan al-Tirmithi , Hadeeth number 2149.
5. Sunan Abi Dawood , Hadeeth number 3731 and 3732.
6. Al-Mustadrak Alal Saheehayn by al-Hakim al-Neesabori , Hadeeth number 6586, and 6589 and 8529.
7. Al-Bayhaqi in Dala'il al-Nubowwah , Hadeeth number 2580 and 2888 and 2889 and 2895.
And in many other Sunni books.