Sinan bin Salamah narrated from his father (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is on a journey on a mount, and comes to a place where he is well fed, let him fast wherever Ramadan reaches him."
Al-Bukhari said: Abd al-Samad bin Habib is munkar al-hadith (his narrations are rejected) and discarded; and al-Bukhari did not consider this hadith to be anything.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8169