Sa'id bin Jubayr (may Allah have mercy on him) narrates that Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both) said to Sayyiduna Mu'awiyah (may Allah be pleased with him), in the conversation that took place between them concerning the pledge of allegiance to Yazid bin Mu'awiyah: "O Mu'awiyah, it was you who narrated to me that the Messenger of Allah (peace and blessings be upon him) said: 'When there are two caliphs on the earth, kill one of them.'"
Imam al-Tabarani (may Allah have mercy on him) said: "Only Sa'id bin Jubayr narrated this hadith from Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both), and only Abu Bishr from Sa'id, and only Sa'id bin Bashir from Abu Bishr, and Zayd bin Yahya bin Ubayd is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب العين / 3885
Hadith Takhrij«أخرجه الطبراني فى «الكبير» برقم: 710»