Narrated from Sayyida Aisha (may Allah be pleased with her), the wife of the Messenger of Allah (ﷺ), that the Messenger of Allah (ﷺ) entered my room and I said: "We have kept something hidden for you." So he (ﷺ) said: "I had intended to fast (but then broke the fast)." He (ﷺ) said: "But soon I will fast a day in place of this fast." Imam Shafi'i (may Allah have mercy on him) said: I used to hear this hadith from Sufyan bin 'Uyaynah (may Allah have mercy on him) in general gatherings, but he would not mention the words "soon I will fast a day in place of this fast." Then, I read this hadith to him a year before his death, and he added these words: "Soon I will fast a day in place of this fast."
Hadith Referenceالسنن المأثورة / باب ما جاء في الأذان / 290
Hadith Takhrijسنن ابی داؤد، الصوم، باب في الرخصة في ذلك، رقم : 2455 وقال الالباني: حسن صحيح سنن ترمذى، الصوم، باب صيام المتطوع بغير تبييت، رقم : 734 وقال حسن