Though the voice from sky is claimed as a convinced sign but there is a discrepancy in the event time. According to a narration from Muhammad al-Baqir this voice will be heard in Ramadan before reappearance of Muhammad al-Mahdi. In compliance with Al-Shaykh Al-Mufid, as well as others, there is a Hadith which state a synchronicity between reappearance of Muhammad al-Mahdi and the voice from sky.