Musannaf Ibn Abi Shayba 37:545

Abdullah ibn Numayr narrated to us, he said: Musa al-Juhani narrated to us, he said: Umar ibn Qays al-Masir narrated to me, he said: Mujahid narrated to me, he said: A certain man from the companions of the Prophet, may Allah bless him and grant him peace, narrated to me that the Mahdi will not emerge until the Pure Soul (al-nafs al-zakiyyah) is killed. When the Pure Soul is killed, those in the heavens and those on the earth will be angry with them. Then the people will come to the Mahdi and lead him like a bride is led to her husband on the night of her wedding. He will fill the earth with equity and justice, the earth will bring forth its vegetation, the sky will pour down its rain, and my nation will enjoy in his reign a bounty the like of which they have never enjoyed before.