´It was narrated that ‘Atiyyah bin Sufyan bin ‘Abdullah bin Rabi’ah said:` “Our delegation who went to the Messenger of Allah (ﷺ) to announce the Islam of Thaqif told us that they came to him in Ramadan. He set up a tent for them in the mosque, and when they became Muslim, they fasted what was left of the month.”
Hadith Referenceسنن ابن ماجه / كتاب الصيام / 1760
Hadith Gradingالألبانی:ضعيف | زبیر علی زئی:ضعيف, إسناده ضعيف, عيسي بن عبد اللّٰه: مقبول (تقريب: 5304) أي مجهول الحال،وثقه ابن حبان وحده فيما أعلم, انوار الصحيفه، صفحه نمبر 442
Hadith Takhrij« تفرد بہ ابن ماجہ ، ( تحفة الأشراف : 15644 ، ومصباح الزجاجة : 632 ) ( ضعیف ) » ( اس کی سند میں محمد بن اسحاق مدلس ہیں ، اور روایت عنعنہ سے کی ہے ، اور عیسیٰ بن عبد اللہ مجہول ہیں )
Brief Explanation
1؎ : There is consensus that if a disbeliever becomes Muslim during Ramadan, he should fast for the remaining days of Ramadan, but making up (qada) for the previous fasts is not obligatory upon him.
Explanation & Benefits
Maulana Ataullah Sajid
Benefit: The aforementioned narration, although weak in its chain of transmission, yet the issue stated therein—that after accepting Islam, he observed the remaining days of fasting in the blessed month of Ramadan— is correct. Because after becoming Muslim, fasting becomes obligatory.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 1760