In one narration the words are: Sayyiduna Sa'd (may Allah be pleased with him), the freed slave of the Prophet (peace and blessings be upon him), narrated this hadith to me: that the people were ordered to fast. Ahmad recorded all of these narrations. Abu Ya'la recorded a similar narration, and its chain contains a narrator who has not been named.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5010