The following Hadith, commonly quoted by Shia, is found in al-Mustadrak:
“Ahlul Bayt are like the Ark of Noah. Whoever embarked on it was saved. Whoever turned away perished.”
However, it is inauthentic. Imam al-Dhahabi said in the Talkhis of al-Mustadrak that this Hadith is a forgery. The Isnad of the Hadith contains Mufaddal ibn Salih, who Shaikh al-Islam Ibn Hajar in his Taqrib called “weak” and whom Imam Bukhari referred to as “Munkhar al-Hadith”. No version of this Hadith contains an acceptable chain of narrators.
In any case, if we were to accept this Hadith as authentic, then it would be used first and foremost in relation to the Prophet’s wives who have most right to being called Ahlel Bayt. The Shia are the ones who have abandoned the Prophet’s wives. If Ahlel Bayt are an Ark, then the Shia have cut up that ship and punched a hole in part of it so that now the entire boat is drowning. On the other hand, the Ahlus Sunnah loves and respect “the entire boat” (i.e. the entirity of the Ahlel Bayt).