Well, the Hijri date 21 Rabi Al Thani 1405 corresponds to the Gregorian date Saturday, 12 January 1985. This date lies in the fourth month of the Hijri year 1405 AH, which is Rabi Al-Thani of 1405 AH. Both this Hijri and Gregorian date occur on the single day that is Saturday without any doubt. The Arabic date 1405/04/21 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 12 January 1985 to its equivalent Arabic date.
The following is the conversion of the Arabic date 21 Rabi Al Thani 1405 AH to its equivalent Gregorian date.
وَقُلِ ٱعْمَلُوا۟ فَسَيَرَى ٱللَّهُ عَمَلَكُمْ وَرَسُولُهُۥ وَٱلْمُؤْمِنُونَ ۖ وَسَتُرَدُّونَ إِلَىٰ عَٰلِمِ ٱلْغَيْبِ وَٱلشَّهَٰدَةِ فَيُنَبِّئُكُم بِمَا كُنتُمْ تَعْمَلُونَ
And say (unto them): Act! Allah will behold your actions, and (so will) His messenger and the believers, and ye will be brought back to the Knower of the Invisible and the Visible, and He will tell you what ye used to do.
Surah At-Tawba(9:105)