Shia narrations in Sunni books

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There has not appeared via authentic isnads, hadiths testifying to the virtues of any Companion like what has appeared testifying to the virtues of Ali b. Abi Talib. ~ Ahmad ibn Hanbal

Sunni source; Ibn Abi Ya’la, Tabaqat al-hanabila, vol. 2, page 156.

As narrated to us by Jabir ibn Abdullah, the Prophet ((صلى الله عليه وآله وسلم)) said;

Ali b. Abi Talib is the earliest to embrace Islam in my community, the most knowledgeable of them, the most correct in his religion, the most virtuous in his certainty, the most prudent, generous and brave of heart, and he is the imam and caliph after me. 

Shia source; Shaykh al-Saduq, Amali al-saduq, p. 7. 

The same hadith can be found in many Sunni collections, even early ones such as the Musannaf of al-Sanani and the Musnad of ibn-Hanbal. However, with absence of the last section referring to Imam Ali (عليه السلام) as a Caliph and Imam. 

Other hadiths such as Ghadir Khumm, ruled by al-Tirmidhi and al-Hakim al-Naysaburi to be sahih (authentic), and the hadith of two weighty things (Quran and Ahlul Bayt) ruled by al-Hakim, Ibn Khuzayma, Muslim b. al-Hajjaj to be sahih (authentic). Among some, al-Naysaburi declared the hadith narrated from the Prophet ((صلى الله عليه وآله وسلم)) “O Fatima, Allah is angered when you are angered, Allah is pleased when you are pleased”, to be sahih (authentic). 

Many times Shia narrations were openly stolen and incorporated into the Sunni books by giving them different authorship. For example, Shaykh al-Saduq quoted (Amali, p. 6) Imam Muhammad al-Baqir (عليه السلام) that the Prophet ((صلى الله عليه وآله وسلم)) had said that the best of Allah’s (سُبْحَانَهُ وَ تَعَالَى) slaves are those “Who, when they seek perfection in their acts, hope for good tidings, seek forgiven when they do wrong, are thankful to Allah (سُبْحَانَهُ وَ تَعَالَى) when they give, persevere when they are tired, and forgive when they are angered.” The same hadith can be found in Hilyat al-awliya (volume 6, page 120) by Abu Nuy’am but through a very Sunni isnad. Shaykh al-Saduq died before Abu Nuy’am. 

Overall, at least 100 Shia narrators found themselves in the major Sunni “authentic” books. In rijal alshi'ah fii asaneed alsunnah we can find the names of 140 of them. al-Muraja’at lists 100 of them. For example, narrations from Adi ibn Thabit al-Kufi can be found in Sunan ibn Majah and other books. Ibn Ma`in has described him as a "Shi`a extremist," while Dar Qutni calls him "Rafidi, extremist, but also reliable." Al-Mas`udi says, "We have never seen anyone who is so outspoken in preaching his Shi`a views like `Adi ibn Thabit."