Sayyiduna Anas (may Allah be pleased with him) narrates that Sayyiduna Abu Talhah (may Allah be pleased with him) was unable to fast during the time of the Messenger of Allah (peace and blessings be upon him) because of the military expeditions. When he (peace and blessings be upon him) passed away, he was never seen without fasting except on the Day of Fitr and the Day of Nahr (Sacrifice).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8485