Hadith No: 1

It has been narrated on the authority of Aba Sa'id al-Khudri that the Messenger of Allah (s.a.w.a.) said:

When oath of allegiance has been taken for two caliphs, kill the one for whom the oath was taken later.

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Reference: Saheeh Muslim Book 33 Tradition No. 96

Hadith No: 2
Abu Awana - Mustakhrij Abi Awana
Kitab al-Hudud - Clarification of the Obligation to Support the Caliph if He is Pledged in Favor of Another...
Volume: (4) - Page Number: (411)
7133 - Abu Umayya narrated to us; he said: Amr ibn Aun al-Wasiti narrated to us; he said: Khalid ibn Abdullah narrated to us, from al-Jariri, from Abu Nadra from Abu Sa'id al-Khudri (may Allah be pleased with him) from the Prophet (peace be upon him and his holy progeny): "If allegiance is pledged to two caliphs, kill the latter of the two."

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Reference: Mustakhraj Abi 'Awwaana Book 4

Hadith No: 3
Al-Bayhaqi - Sunan al-Kubra - Book on Fighting the People of Rebellion
Summary of the Chapters on Shepherds - Chapter on Two Imams Not Being Suitable in One Era
Volume: (8) - Page Number: (248)
16547 - Abu al-Hasan Ali ibn Ahmad ibn Abdān narrated to us, saying: Ahmad ibn Ubayd al-Saffar narrated to us, saying: Ibn Abi Qumash narrated to us, saying: Amr ibn Aun narrated to us from Khalid, and Abu Abd Allah al-Hafiz narrated to us, saying: Abu Bakr ibn Abdullah informed me, saying: al-Hasan ibn Sufyan narrated to us, saying: Wahb ibn Baqiyya narrated to us, saying: Khalid ibn Abdullah narrated to us from al-Jurayri from Abu Nadrah from Abu Sa'id, who said: The Messenger of Allah (peace be upon him and his holy progeny) said: "When allegiance is pledged to two caliphs, kill the latter of them." This was also narrated by Muslim in the Sahih from Wahb ibn Baqiyya.

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Reference: Al-Sunan al-Kubra Book 8

Hadith No: 4
Al-Tabarani - Al-Mu'jam al-Awsat - Chapter on the letter Alif - Section on those named Ibrahim
Volume: (3) - Page Number: (144)
2743 - Ibrahim said: Ammar ibn Harun narrated to us, he said: Abu Hilal narrated to us, from Qatadah, from Sa'id ibn al-Musayyib from Abu Huraira, who said: The Messenger of Allah (peace be upon him and his holy progeny) said: "If allegiance is pledged to two caliphs, kill the younger of the two." This hadith was not narrated from Qatadah except by Abu Hilal.

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Reference: Al-Mo'jam al-Awsat Book 3