The most excellent fast after Ramadan is Allah's month, Muharram, and the most excellent prayer after what is prescribed is prayer during the night. [Muslim]
"«أفضل الصِّيام، بعد رمضان، شَهر الله المُحَّرم، وأفضل الصلاة، بعد الفَريضة، صلاة الليل». [صحيح.] - [رواه مسلم.]"
