Talhah bin Ubaidullah (may Allah be pleased with him) narrates that a man came to the Messenger of Allah (ﷺ), asking about Islam. The Messenger of Allah (ﷺ) said: “(Islam) is to perform five prayers in the day and night.” He said: “Is there any prayer obligatory upon me besides this?” The Prophet (ﷺ) said: “No, except if you offer voluntary prayers.”
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 116
Hadith Takhrijاخرجه البخاري: الايمان، باب الزكاة من الاسلام (46، 1891) ومسلم، الايمان، بيان الصلوات التي هي احد اركان الاسلام (11)