Well, the Hijri date 20 Shawwal 1399 corresponds to the Gregorian date Tuesday, 11 September 1979. This date lies in the tenth month of the Hijri year 1399 AH, which is Shawwal of 1399 AH. Both this Hijri and Gregorian date occur on the single day that is Tuesday without any doubt. The Arabic date 1399/10/20 is calculated using the Umm Al-Qura calendar and the sighting of the moon. One thing to remember is that this Arabic date may occur on different Gregorian date depending upon the region and country and obviously the moon.
If you are still not sure about the date then you can use our Arabic date converter.
The following is the conversion of the Gregorian date 11 September 1979 to its equivalent Arabic date.
The following is the conversion of the Arabic date 20 Shawwal 1399 AH to its equivalent Gregorian date.
أَلَمْ يَأْتِكُمْ نَبَؤُا۟ ٱلَّذِينَ مِن قَبْلِكُمْ قَوْمِ نُوحٍۢ وَعَادٍۢ وَثَمُودَ ۛ وَٱلَّذِينَ مِنۢ بَعْدِهِمْ ۛ لَا يَعْلَمُهُمْ إِلَّا ٱللَّهُ ۚ جَآءَتْهُمْ رُسُلُهُم بِٱلْبَيِّنَٰتِ فَرَدُّوٓا۟ أَيْدِيَهُمْ فِىٓ أَفْوَٰهِهِمْ وَقَالُوٓا۟ إِنَّا كَفَرْنَا بِمَآ أُرْسِلْتُم بِهِۦ وَإِنَّا لَفِى شَكٍّۢ مِّمَّا تَدْعُونَنَآ إِلَيْهِ مُرِيبٍۢ
Hath not the history of those before you reached you: the folk of Noah, and (the tribes of) A'ad and Thamud, and those after them? None save Allah knoweth them. Their messengers came unto them with clear proofs, but they thrust their hands into their mouths, and said: Lo! we disbelieve in that wherewith ye have been sent, and lo! we are in grave doubt concerning that to which ye call us.
Surah Ibrahim(14:9)
