Abu Qays, the freed slave of Amr, narrated: Sayyiduna Amr (may Allah be pleased with him) used to keep voluntary fasts continuously.
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5164