Divine Will and Qadr (Predestination)

أَوْ يُزَوِّجُهُمْ ذُكْرَانًا وَإِنَـٰثًا ۖ وَيَجْعَلُ مَن يَشَآءُ عَقِيمًا ۚ إِنَّهُۥ عَلِيمٌ قَدِيرٌ

Or He makes them [both] males and females, and He renders whom He wills barren. Indeed, He is Knowing and Competent.