سنن النسائي

It was narrated that Saeed bin Al-Musayyab said: "The Messenger of Allah (ﷺ) said: 'It is not righteousness to fast when traveling."' (Sahih) Abu 'Abdur-Rahman (An-Nasai) said: This is a mistake, and what is correct is the one that is before it. We do not know of anyone who followed up Ibn Kathir.