Sayyiduna Jabir bin Abdullah (may Allah be pleased with both of them) narrates: The Prophet Muhammad (peace and blessings be upon him) saw a man during a journey who was under the shade of a tree, and water was being sprinkled on him. The Prophet (peace and blessings be upon him) inquired: "What has happened to your companion?" The people replied: "O Messenger of Allah! He is observing a fast." The Prophet (peace and blessings be upon him) said: "Fasting during travel is not an act of righteousness. It is obligatory upon you to accept the concession that Allah Almighty has granted you."
Hadith Referenceصحیح ابن حبان / كتاب البر والإحسان / 355
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «التعليق الرغيب» (2/ 90).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط البخاري.