Salam alaykom wa rahmatullah wa barakatu :)
It’s flawed reasoning to believe this is a belief that only Shias uphold.
- In Sahih Muslim - a book the Ahle Sunnah revere as one of the six major texts after the Quran, we find the following hadith:
"Zaid bin Arqam, narrated that the messenger of Allah said, ‘Indeed, I am leaving among you, that which if you hold fast to them, you shall not be misguided after me. One of then is greater than the other: (First is) The book of Allah is a rope extended from the sky to the earth, and (the second is) my family, the people of my house (ahlul bait), and they shall not split until they meet me at the hawd, so look at how you deal with them after me.’" - Sahih Muslim, Volume 6, Chapter 31, Hadith No. 3788
"Jibir bin Abdullah said, ‘I saw the Messenger of Allah during his Hajj, on the Day of Arafah (on his last pilgrimage). He was upon his camel Al-Qaswa, giving a Khutbah, so he said: O People! Indeed, I have left among you, that which if you hold fast to it, you shall not go astray: The Book of Allah (Quran) and my Family, the People of my House (Ahlul-Bait).’" - Sahih Muslim, Volume 6, Chapter 31, Hadith No. 3786
- Regarding the 12 succesors:
Sahih Bukhari: Narrated Jabir bin Samura: I heard Muhammad saying, “There will be twelve Muslim rulers.” He then said a sentence which I did not hear. My father said, “All of them (those rulers) will be from Quraish.”
Sahih Muslim: Narrated Jabir bin Samura: I heard Muhammad saying, “The (Islamic) religion will continue until the Hour (day of resurrection), having twelve Caliphs for you, all of them will be from Quraysh.”
Sunan Abu Dawood: The Prophet said: “This religion remains standing until there are twelve vicegerents over you, all of them agreeable to the nation, all of them from Quraysh.”
Sunan al-Tirmidhi: The Prophet said: “There will be after me twelve Amir (Prince/Ruler), all of them from Quraysh.”
Musnad Ahmad ibn Hanbal: Mashrooq rates that someone asked Abdullah Ibn Masood, “O Abaa Abd al-Rahmaan, did you ask the Messenger of Allah how many caliphs will rule this nation?”. Abdullah Ibn Masood replied, “Yes, we did ask the Messenger of Allah and he replied, “Twelve, like the number of chiefs (nuqabaa) of Bani Israel”
- Appointed successor:
"Sheikh Sulayman Balkhi Hanafi in his Yanabiu’l-Mawadda, ch.76, reports from Fara’idu’s-Simtain of Hamwaini, who reports from Mujahid, who reports from Ibn Abbas: A Jew named Na’thal came to Muhammad and asked him questions about Tawhid (Unity of Allah). Muhammad answered his questions and the Jew embraced Islam. Then he said, ‘O Holy Prophet, every prophet had a wasi (vicegerent). Our Prophet, Moses Bin Imran, made a will for Yusha Bin Nun. Please tell me who is your wasi?’ The Holy Prophet said, ‘My vicegerent is Ali Bin Abi Talib; after him are Hasan, and Husain and after them are nine Imams, who are the successive descendants of Husain.’"
"Ahmad ibn Muhammad al-Tha’labi in his Manaqib and Tafsir, Ibn Maghazili Faqih Shafi’i in his Manaqib and Mir Seyyed Ali Hamadani in his Mawaddatu’l-Qurba (Mawadda VI) narrate from the Second Rightly-Guided Caliph, Umar bin Khattab, who, when the Muhammed established fraternal and brotherly ties between the companions, said, ‘This Ali is my brother in this world and in the hereafter. Among my descendants he is my caliph; he is my successor (vicegerent) in my community. He is the heir to my knowledge; he is the payer of my debt. What belongs to him belongs to me; what belongs to me belongs to him; his benefit is my benefit and his loss is my loss. He who is a friend of his is really a friend of mine and he who is an enemy of his is really an enemy of mine."
- Let’s look at other texts respected by Ahle Sunnah:
"Muhammad said, ‘One of them (i.e. the Thaqalayn) is the Book of Allah and the other one is my select progeny (Itrat), that is family (Ahlul-Bayt). Beware of how you behave (with) them when I am gone from amongst you, for Allah, the Merciful, has informed me that these two (i.e., Quran and Ahlul-Bayt) shall never separate from each other until they reach me in Heaven at the Pool (of al-Kawthar). I remind you, in the name of Allah, about my Ahlul-Bayt. I remind you, in the name of Allah, about my Ahlul-Bayt. Once more! I remind you, in the name of Allah, about my Ahlul-Bayt.’" - A’alam al-Wara, pp 132-133
- In the event of Ghadir, RasulAllah (saww) said, “O Allah! For whomsoever I am master ‘Ali is his master. O Allah! befriend his friends and despise his enemies)”. - Al-Musnad Ahmad Ibn Hanbal, hadith no. 950
This isn’t narrated just once. On the contrary, “Ibn Hanbal has recorded the event of Ghadir over 30 times in his Musnad through different isnad or chains of authority and in the words of more than 10 companions of the Prophet.” - Al-Salafi, Murshid al-Muhtar, vol. 3, pp. 156-157.
"Don’t try to find faults with ‘Alī, he is indeed from me and I am from him, he is your leader after me. He is from me and I am from him, he is your leader after me." - Ibn Hanbal’s Musnad, vol. 5, 356, Matba‘ah al-Maymaniyyah
- In the event of Mubahila:
"This hadith has been narrated. on the authority of Shu’ba with the same chain of transmitters. Amir b. Sa’d b. Abi Waqqas reported on the authority of his father that Muawiya b. Abi Sufyin appointed Sa’d as the Governor and said: What prevents you from abusing Abu Turab (Hadrat ‘Ali), whereupon be said: It is because of three things which I remember Allah’s Messenger (may peace be upon him) having said about him that I would not abuse him and even if I find one of those three things for me, it would be more dear to me than the red camelg. I heard Allah’s Messenger (may peace be upon him) say about ‘Ali as he left behind hrin in one of his campaigns (that was Tabuk). ‘All said to him: Allah’s Messenger, you leave me behind along with women and children. Thereupon Allah’s Messenger (may peace be upon him) said to him: Aren’t you satisfied with being unto me what Aaron was unto Moses but with this exception that there is no prophethood after me. And I (also) heard him say on the Day of Khaibar: I would certainly give this standard to a person who loves Allah and his Messenger and Allah and his Messenger love him too. He (the narrator) said: We have been anxiously waiting for it, when he (the Holy Prophet) said: Call ‘Ali. He was called and his eyes were inflamed. He applied saliva to his eyes and handed over the standard to him, and Allah gave him victory. (The third occasion is this) when the (following) verse was revealed:" Let us summon our children and your children." Allah’s Messenger (may peace be upon him) called ‘Ali, Fitima, Hasan and Husain and said: O Allah, they are my family.’" - Sahih Muslim Book 031, Number 5915
"Saad bin Abi Waqas relates that when the Ayat-e-Mubahila was sent down, Prophet Mohammad(sawaw) called Imam Ali(a.s.), Bibi Fatima(s.a.), Imam Hasan(a.s.) and Imam Hussain(a.s.) and said, ‘O my Allah(swt), these are my Ahl-e-Bait.’" - Sahih Muslim, Vol.2, Page 287
I hope this answers your inquiry in depth. Thank you for your question cause it refreshed my memory. Ya Ali (as). :)