Hadith.1974 - Ubayd ibn Zurara asked Abu Abdullah (as) about the verse of Allah (swt), the Exalted:
"So whoever among you witnesses the month, let him fast it." (Surah Al-Baqarah 2:185)
Imam (as) replied: "How clear it is! Whoever is present (not traveling) should fast it, and whoever is traveling should not fast it."