Ash Shaykh Zayid Al Wusaabee mentioned:
Was Ramadan obligated upon those before us from the nations?
Allah Ta’ala said:
يَا أَيُّهَا الَّذِينَ آمَنُواْ كُتِبَ عَلَيْكُمُ الصِّيَامُ كَمَا كُتِبَ عَلَى الَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ
O you who believe! Observing As-Saum (the fasting) is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqun (the pious – see V.2:2) [2:183]
Those before us are the Jews and it is the statement of Ibn Abbas رضي الله عنه.
It is said by some that they are the Christians. It is by others that they are the Jews and the Christians. It is said by others that it is more general and thus it includes everyone who Allah sent a messenger to and sent down upon them a book. This view is closer [to being correct]
Was Ramadan obligatory upon them?
It came from Qatadah that Allah obligated Ramadan upon those before us. Ibn Jareer reported it. As for from the prophet صلى الله عليه و سلم, nothing has been affirmed. Since nothing has been affirmed, we say fasting was obligated upon them but Allah knows best how that fast was obligated upon them.
It comes from Ibn Abbas رضي الله عنهما that when the prophet صلى الله عليه و سلم came to Madeenah, the Jews would fast Ashuraa and they would say that is is the day which Allah saved Musa in. So the prophet صلى الله عليه و سلم said we have more right to Musa than them. And he commanded that it be fasted. [Reported by Al Bukhari 2004 and Muslim 1130]
[Miskul Khitaam 2/402]
Majid Jawed Al-Afghanee