Abu Nadrah says: A young man from the tribe of Aslam asked Sayyiduna Imran bin Husayn (may Allah be pleased with him) about the prayer of the Prophet (peace and blessings be upon him), and he replied: Whenever the Prophet (peace and blessings be upon him) travelled, he prayed only two rak'ahs, except for the Maghrib prayer.
(Allamah al-Haythami says:) I say: Abu Dawud and others recorded this narration, but they did not mention the Maghrib prayer.
Ahmad recorded it.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2943