Some people claim that the exact date of birth of the Prophet (صلى الله عليه وآله وسلم) is not known and hence there is little room for the celebration of Eid-e-Milad-un-Nabi (صلى الله عليه وآله وسلم) on 12th of Rabi-ul-Awal.
12 Rabi-ul-Awal is not only accepted as Milad Day from the classical and ancient scholars, it is also confirmed by the governments of the whole Islamic world. The holidays of almost 2 dozen Islamic countries, and except Iran ALL other countries celebrate it on 12 Rabi-ul-Awal. Iran celebrates it on 17 Rabi-ul-Awal, but this is because they coincide it with the birth date of Imam Jafar Sadiq (علیھ السلام).
Opinion of Renowned Historians about the Authentic Date of Milad
1. Imam Ibn-e-Ishaq (85-151 H): Messenger of Allah (صلى الله عليه وآله وسلم) was born on 12 Rabi-ul-Awal in Aam-ul-Feel. (Ibn-e-Jozi in Al-Wafa, Page 87)
2. Allama Ibn-e-Hasham (213 H): Messenger of Allah (صلى الله عليه وآله وسلم) was born on Monday 12 Rabi-ul-Awal in Aam-ul-Feel. (Ibn-e-Hasham in As-Sirat-un-Nabawiya, Vol. 1, Page 158)
3. Imam Ibn-e-Jareer Tabari (224-310 H): Messenger of Allah (صلى الله عليه وآله وسلم) was born on Monday 12 Rabi-ul-Awal in Aam-ul-Feel. (Tarikh-ul-Umam-wal-Muluk, Vol. 2, Page 125)
4. Allama Abu-ul-Hasan Ali Bin Muhammad Al-Mawardi (370-480 H): Messenger of Allah (صلى الله عليه وآله وسلم) was born 50 days after the event of Ashab-ul-Feel and after the death of His father on Monday 12 Rabi-ul-Awal. (Ailam-un-Nabuwa, Page 192)
5. Imam Al-Hafiz Abu-ul-Fatah Al-Undalasi (671-734 H): Our leader and our Prophet Muhammad (صلى الله عليه وآله وسلم), the Messenger of Allah, was born on Monday 12 Rabi-ul-Awal in Aam-ul-Feel. (Aayun-al-Asr, Vol.1, Page 33)
6. Allama Ibn-e-Khaldun (732-808 H): Messenger of Allah (صلى الله عليه وآله وسلم) was born on 12 Rabi-ul-Awal in Aam-ul-Feel. It was the 40th year of Emperor Kasra Noshairwan. (Ibn-e-Khaldun in At-Tarikh Vol. 2, Page 394)
7. Muhammad As-Sadiq Ibrahim Arjoon: From various turaq (chains) it has been established as true that the Prophet (صلى الله عليه وآله وسلم) was born on Monday 12 Rabi-ul-Awal in Aam-ul-Feel in the reign of Kasara Noshairwan. (Muhammad Rasool Ullah, Vol. 1, Page 102)
8. Sheikh Abdul-Haq Muhadath Dehlvi (950-1052 H):Know it well, that over-whelming majority of the experts of sayar and tarikh (i.e. biographers and historians) hold the opinion that An-Hazrat (i.e. the prophet صلى الله عليه وآله وسلم) was born in Aam-ul-Feel … It is well known that the month was of Rabi-ul-Awal and its date was 12. Various scholars have shown their agreement with this (date). (Madarij-un-Nabuwa, Vol. 2, Page 14)
9. Nawab Muhammad Sadiq Hasan Khan Bohapalvi: The birth (of the Prophet صلى الله عليه وآله وسلم) was happened in Makkah at the time of Fajar on Monday 12 Rabi-ul-Awal in Aam-ul-Feel. Majority of scholars holds this opinion. Ibn-e-Jozi has narrated a consensus (of scholars) on it. (Ash-Shumama-tul-Anbariya Fi Mowlid Khair-al-Bariya, Page 7)
You can see that the historians / scholars from the first / second century of Hijri, as well as the scholars of later times, had been authenticating it. The list also includes the well known leader of Salafis, i.e. Nawab Sadiq Hasan Bohapalvi.
This Date is Officially Recognized by Islamic World
Milad-un-Nabi (صلى الله عليه وآله وسلم) is celebrated throughout the Islamic world, with the exception of a few countries. Interestingly, all the Islamic countries (except Iran, whose reason I mentioned above) celebrate it on 12th of Rabi-ul-Awal.
The most authentic date of Milad-un-Nabi (i.e. Prophet (صلى الله عليه وآله وسلم)'s birth), as agreed upon by the classical and later scholars and historians, and as officially recognized by Islamic countries, is Monday 12 Rabi-ul-Awal.
Now Im going to prove from a scholar whom even Salafi consider the top most scholar in Tafsir and Tarikh and he not only says 12th is the mainstreem opinion but also relies with exact hadith for it
ورواه ابن أبى شيبة في
مصنفه عن عفان ، عن سعيد بن ميناء ، عن جابر وابن عباس أنهما قالا : ولد رسول الله
صلى الله عليه وسلم عام الفيل يوم الاثنين الثانى عشر من شهر ربيع الاول
Translation: Ibn Abi Shaybah (rahmatullah taala aleyh) in his Musannaf narrates from Affan>>Sa’id>>Jabir and Ibn Abbas (ridhwan Allahu ajmain) who said: Rasul Ullah (salallaho alaihi wasalam) was born in the year of elephant on Monday, the 12th Rabi Ul Awwal [Ibn Kathir in Seerat un Nabi, Volume 1, Page No. 199]
Then he said:
وهذا هو المشهور عند الجمهور
والله أعلم .
This is what is famous amongst Majority and Allah knows the best [ibid]
Imam Qastallani (rahimuhullah) said: Rasul Ullah (sal-lal-lahu alai hi wa sallam) was born on 12th Rabi ul Awwal and People of Makkah follow it,on this same day they visit (your place of birth).. It is famous that you were born on 12th Rabi ul Awwal, the day was of Monday, Ibn Ishaq (rah) and others have narrated this too [Al Muwahib al Laduniya, Volume 1, Page No. 88]