The Prophet (PBUH&HF) said: "Allah will bring out from concealment al-Mahdi from my Family and just before the Day of Judgment; even if only one day were to remain in the life of the world, and he will spread on this earth justice and equity and will eradicate tyranny and oppression."
Sunni reference: Musnad Ahmad Ibn Hanbal, v1, p99
The Messenger of Allah said: "The stars are amnesty for the inhabitants of the heavens, and if the stars go away (i.e., become non-existent), the inhabitants of the heavens will be destroyed. And my Ahlul-Bayt are amnesty for the inhabitants of the earth, and if my Ahlul-Bayt go away (i.e., all die), the inhabitants of the earth will be destroyed."
Sunni references:
Fadha'il al-Sahaba, by Ahmad Ibn Hanbal, v2, p671, Tradition #1145
Dhakha'ir al-Uqba, by Muhibbuddin al-Tabari, p14
Manaqib Ahmad, and many more such as al-Tabarani, etc.
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p234
Musnad, Abu Ya'ala, on the authority of Salama Ibn Awka' in which the wording is: "The stars are amnesty for the inhabitants of the heavens, and my Ahlul-Bayt are the amnesty for my Ummah."
"In every generation of my followers there are going to be just and righteous members of my Ahlul-Bayt to counteract the alterations and corruption's which the misguided people will try to make in my religion, to remove the false allegations of the untruthful and contradict the misinterpretations of the ignorant. Be aware! Your Imam shall be your representative before Allah, so be careful whom you adopt as your representative."
Sunni reference: al-Sawa'iq al-Muhriqah, by Ibn Hajar, Ch. 11, section 1, p231 under the commentary of verse: "And stop them, for they shall be questioned! [37:24]"
"The traditions which describe the necessity of adherence to Ahlul-Bayt until the day of Judgment, also imply that the existence of the righteous members of the family of the Prophet will NOT terminate until the day of Judgment the same way as the Book of Allah will remain."
Sunni reference: al-Sawa'iq al-Muhriqah, by Ibn Hajar, Ch. 11, section 1, p232