Translation of the verse 81 from Surah Az-Zukhruf : Number of verses 89 - - page 495 - Part 25.
Say (O Muhammad SAW): "If the Most Beneficent (Allah) had a son (or children as you pretend), then I am the first of Allah's worshippers [who deny and refute this claim of yours (and the first to believe in Allah Alone and testify that He has no children)]." [Tafsir At-Tabari].
Say, [O Muhammad], "If the Most Merciful had a son, then I would be the first of [his] worshippers."
(43:81) Say: 'If the Merciful One had a son, I would have been the first one to worship him.' *64
*64) It means: "My rejection of somebody's being God's offspring and my refusal to worship those whom you regard as His offspring is not due to any stubbornness and obduracy. My reason for the refusal is only this that God has no son or daughter, and your such beliefs are against the reality; otherwise I am such a faithful servant of my Lord that if at all the reality had been the same as you state I would have submitted myself in worship before you. "