Heavenly Cry (Arabic: الصيحة) is among the signs before the Reappearance of Imam al-Mahdi (a). This call is made by Gabriel and will be heard from the sky. The message in this call has been mentioned in different ways: giving glad news about the Reappearance of Imam al-Mahdi (a), his description, and the rightfulness of Shi'a. At the end of the same day, Satan will try to make doubts in people using a similar call. Hadiths regarding the Heavenly Cry are mutawatir, but they have mentioned different times for it.
Hearing the miraculous Heavenly Cry has been regarded among the signs of the reappearance or uprising of Imam al-Mahdi (a). This call will be made by Gabriel and in Shia and Sunni sources, it has been referred to as "nida'" (Arabic:نداء) [call], "sayha" (Arabic:صیحة) [scream] and "sawt" (Arabic:صوت) [sound] among which, "nida'" has been more frequent in hadiths. In Arabic, "nida'" means "to raise and show a voice" and "sayha" means "a loud sound or cry". Although in many hadiths, "sayha" has been referring to "nida'" but in some, they have been regarded as two different phenomenon.
According to al-Shaykh al-Saduq's narration from Imam al-Sadiq (a), this sign beside four other signs (uprising of al-Sufyani, uprising of al-Yamani, al-Khasf bi-l-Bayda', and murder of al-Nafs al-Zakiyya) is among the certain signs preceding the Reappearance of Imam al-Mahdi (a). In another hadith, the first of these signs has been mentioned to be this Heavenly Cry in the month of Ramadan. Imam Ali (a) said, "Expect the Reappearance in three conditions". Someone asked, "what are those signs?" Imam (a) answered, "the conflicts among the people of Syria; black flags coming from Khorasan, and the Call in the month of Ramadan."
This call made by Gabriel will be heard by all people, so that anyone will hear it in his own language. Most hadiths have mentioned sky as the place of broadcasting this call. One of its attributes is that it will be heard equally from near and far; it will wake up the asleep and scares people; it will bring the faithful mercy and will bring disbelievers pain and from then, the name of Imam al-Mahdi (a) will be distributed among people.
Narrations about the time of the Heavenly Cry are different and have caused different reactions among scholars.
According to the views of most scholars, Heavenly Cry will happen in Ramadan of the year before the Reappearance. Their justification is a hadith from Imam al-Baqir (a) who said,
Form some hadiths, it can be understood that the Heavenly Cry will happen upon the Reappearance of Imam al-Mahdi (a). In these narrations, the happening of the Heavenly Cry coincides with the uprising of Imam (a). Al-Shaykh al-Mufid has mentioned this coincidence in a hadith from the Prophet (s),
Some have regarded the time of Reappearance and the time of uprising to be different from each other. They believe that Heavenly Cries are after the Reappearance and before the uprising and that Heavenly Cries will be several from the Reappearance until the uprising. Mentioning different times for the Heavenly Cry in narrations in some ways support this possibility.
In most narrations, the message of this call has been said to be introducing Imam al-Mahdi (a) with his name and attributes. Also, in some narrations, the message of this call has been mentioned to be declaration of the rightfulness of Imam Ali (a) and the salvation of his followers.
Beside narrations related with the Heavenly Cry, some narrations suggest that toward the end of the same day, Satan will also make a call, the purpose of which is making doubts in people for following Imam al-Mahdi (a), "Behold that the right is with 'Uthman b. 'Affan and his followers. He was killed being oppressed; so, rise to his revenge and know that rights belong to al-Sufyani and his followers and 'Uthman and his followers will be salvaged." With this call, some will become doubtful.
In other narrations, the message of Satan's call has been said to be inviting people to Christianity. Some believe that Satan will also make some calls and each time tries to mislead people. They have deemed it possible that makers of these call would be people who do it following Satan's deception.
Regardless of the many narrations, some writers have tried to interpret this sign in agreement with new technologies and today advances in sciences as satellites. This justification has not been approved by religious scholars due to lack of its evidences.