Can you mention the source for this please?
الليث: عن معاوية بن صالح، أن أبا جبلة حدثه، قال كنت مع ابن شهاب في سفر فصام يوم عاشوراء، فقيل له: تصوم يوم عاشوراء في السفر وأنت تفطر في رمضان؟ قال: إن رمضان له عدة من أيام أخر، وإن عاشوراء يفوت
سير أعلام النبلاء
Answer:
Imam Bayhaqi (rahimahullah) has recorded this narration.
(Shu’abul Iman, Hadith: 3518. Also see: Siyaru A’alamin Nubala, vol. 5 pg. 342)
Translation
Jabalah (rahimahullah) reports, “I was once on a journey with Ibn Shihab (rahimahullah). He fasted on the day of ‘Aashura. Someone asked, ‘You are fasting ‘Aashura while on journey, whereas in Ramadan you [sometimes] do not fast [when on journey]’. Ibn Shihab replied, ‘The fast of Ramadan can be made up [out of Ramadan] but the fast of ‘Aashura cannot.’”
And Allah Ta’ala Knows best.
Answered by: Moulana Suhail Motala
Approved by: Moulana Muhammad Abasoomar