Well, the Hijri date 11 Shawwal 1266 corresponds to the Gregorian date Monday, 19 August 1850. This date lies in the tenth month of the Hijri year 1266 AH, which is Shawwal of 1266 AH. Both this Hijri and Gregorian date occur on the single day that is Monday without any doubt. The Arabic date 1266/10/11 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 19 August 1850 to its equivalent Arabic date.
The following is the conversion of the Arabic date 11 Shawwal 1266 AH to its equivalent Gregorian date.
وَقَدْ مَكَرُوا۟ مَكْرَهُمْ وَعِندَ ٱللَّهِ مَكْرُهُمْ وَإِن كَانَ مَكْرُهُمْ لِتَزُولَ مِنْهُ ٱلْجِبَالُ
Verily they have plotted their plot, and their plot is with Allah, though their plot were one whereby the mountains should be moved.
Surah Ibrahim(14:46)