“The Takbīr (proclamation of ‘Allāhu Akbar’) in the ʿEid of al-Fiṭr is seven times in the first (rakʿah) and five times in the last, and the recitation follows both of them.”

Narrated by Abū Dāwūd (no. 1151) — his wording — and by al-Nasā’ī in al-Sunan al-Kubrā (no. 1817), from the narration of ʿAbd Allāh ibn ʿAmr ibn al-ʿĀṣ (may Allah be pleased with them both).
Authenticated in Ṣaḥīḥ al-Jāmiʿ (no. 3017) and Ṣaḥīḥ Abī Dāwūd (no. 1045).

Brief Explanation of the Hadith

Among the great blessings of Allah Almighty upon His servants is that He has prescribed for them the festivals (aʿyād), and among the most manifest of their symbols is the ʿEid prayer.
In this ḥadīth, ʿAbd Allāh ibn ʿAmr (may Allah be pleased with them both) relates two of the distinguishing features of the ʿEid prayer: First: the additional takbīrs (proclamations of “Allāhu Akbar”), and second: the recitation that follows the takbīr.
The Sunnah is that one pronounces seven takbīrs (proclamations of “Allāhu Akbar”) in the first rakʿah, including the opening takbīrah (takbīrat al-iḥrām), and five takbīrs in the second rakʿah, apart from the takbīrah when rising from prostration.
After that, one recites Sūrat al-Fātiḥah followed by another sūrah. The Sunnah is to recite in the first rakʿah: {Sabbih isma rabbika al-Aʿlā} — “Glorify the Name of your Lord, the Most High” (al-Aʿlā: 1), and in the second: {Hal atāka ḥadīthu al-ghāshiyah} — “Has there come to you the report of the Overwhelming Event?” (al-Ghāshiyah: 1), as reported in Ṣaḥīḥ Muslim from the narration of al-Nuʿmān ibn Bashīr (may Allah be pleased with him).
Alternatively, one may recite in the first rakʿah: {Qāf. Wa’l-Qur’āni al-Majīd} — “Qāf. By the Glorious Qur’an” (Qāf: 1), and in the second: {Iqtarabati al-sāʿatu wa’nshaqqa al-qamar} — “The Hour has drawn near, and the moon has split asunder” (al-Qamar: 1), as reported in the ḥadīth of Abū Wāqid al-Laythī (may Allah be pleased with him).
The Sunnah is to vary the recitation in the two rakʿahs — at times reciting “Sabbih isma rabbika al-Aʿlā” and “Hal atāka ḥadīthu al-ghāshiyah”, and at other times “Qāf. Wa’l-Qur’āni al-Majīd” and “Iqtarabati al-sāʿatu wa’nshaqqa al-qamar.”
Moreover, the Prophet’s — may Allah’s peace and blessings be upon him — statement, “The takbīr in the ʿEid of al-Fiṭr...” does not imply that this ruling is exclusive to the ʿEid of al-Fiṭr; rather, it equally applies to the ʿEid of al-Aḍḥā, for there is no distinction between the two in the manner of performing the prayer.