Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) combined the Maghrib and Ishā' prayers. He prayed three Rak‘ahs for Maghrib then two Rak‘ahs for Ishā' with one Iqāmah

عن ابن عمر رضي الله عنهما ، قال: «جمع رسول الله صلى الله عليه وسلم بين المغرب والعشاء بجمع: صلى المغرب ثلاثاً، والعشاء ركعتين، بإقامة واحدة».
[صحيح] - [رواه مسلم]

Ibn ‘Umar (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) combined the Maghrib and Ishā' prayers. He prayed three Rak‘ahs for Maghrib then two Rak‘ahs for Ishā' with one Iqāmah.
[Authentic hadith] - [Narrated by Muslim]

Explanation

The Hadīth shows the way the Prophet (may Allah's peace and blessings be upon him) combined between the prayers one night when he was at Al-Muzdalifah after his return from ‘Arafah. He combined Maghrib prayer with Ishā' prayer and shortened the latter to two Rak‘ahs only with one Adhān for both and one Iqāmah for each.