Musannaf Ibn Abi Shayba 24:173

Ibn Fudayl narrated to us, from ‘Ata’, who said: Two Eids coincided on one day. Al-Hajjaj said during the first Eid: "Whoever wishes to pray with us may pray, and whoever wishes to leave may leave, and there is no blame." Abu al-Bakhtari and Maysarah said: "What is wrong with him? May Allah kill him! From where did he stumble upon this?"