Well, the Hijri date 18 Shawwal 1399 corresponds to the Gregorian date Sunday, 9 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 Sunday without any doubt. The Arabic date 1399/10/18 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 9 September 1979 to its equivalent Arabic date.
The following is the conversion of the Arabic date 18 Shawwal 1399 AH to its equivalent Gregorian date.
۞ وَإِذَا صُرِفَتْ أَبْصَٰرُهُمْ تِلْقَآءَ أَصْحَٰبِ ٱلنَّارِ قَالُوا۟ رَبَّنَا لَا تَجْعَلْنَا مَعَ ٱلْقَوْمِ ٱلظَّٰلِمِينَ
And when their eyes are turned toward the dwellers of the Fire, they say: Our Lord! Place us not with the wrong-doing folk.
Surah Al-A'raaf(7:47)