Abstain from fasting while travelling if it becomes too difficult or tiring due to the physical exertion involved in the journey.

According to the hadith narrated by Yahya from Malik from Nafi, Abdullah ibn Umar used to abstain from fasting while travelling. This is because fasting can be difficult and tiring during a journey due to the physical exertion involved in travelling. Therefore, it is permissible for a person who is travelling to abstain from fasting and make up for it later when they are no longer on their journey. This hadith teaches us that we should take into consideration our physical limitations when engaging in religious activities such as fasting and that we should not push ourselves beyond our limits.