Well, the Hijri date 13 Jumada Al Akhira 1399 corresponds to the Gregorian date Wednesday, 9 May 1979. This date lies in the sixth month of the Hijri year 1399 AH, which is Jumada Al-Thani of 1399 AH. Both this Hijri and Gregorian date occur on the single day that is Wednesday without any doubt. The Arabic date 1399/06/13 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 May 1979 to its equivalent Arabic date.
The following is the conversion of the Arabic date 13 Jumada Al Akhira 1399 AH to its equivalent Gregorian date.
فَٱصْبِرْ كَمَا صَبَرَ أُو۟لُوا۟ ٱلْعَزْمِ مِنَ ٱلرُّسُلِ وَلَا تَسْتَعْجِل لَّهُمْ ۚ كَأَنَّهُمْ يَوْمَ يَرَوْنَ مَا يُوعَدُونَ لَمْ يَلْبَثُوٓا۟ إِلَّا سَاعَةًۭ مِّن نَّهَارٍۭ ۚ بَلَٰغٌۭ ۚ فَهَلْ يُهْلَكُ إِلَّا ٱلْقَوْمُ ٱلْفَٰسِقُونَ
Then have patience (O Muhammad) even as the stout of heart among the messengers (of old) had patience, and seek not to hasten on (the doom) for them. On the day when they see that which they are promised (it will seem to them) as though they had tarried but an hour of daylight. A clear message. Shall any be destroyed save evil-living folk?
Surah Al-Ahqaf(46:35)