"And by the heaven and He who built it," meaning: and by the One who built it. He swore by the heaven and by Himself.
﴿وَالسَّمَاء وَمَا بناها﴾ أَيْ: وَالَّذِي بَنَاهَا، أَقْسَمَ بِالسَّمَاءِ وبنفسه
