(43:81) Say, [O Muhammad], “If the Most Merciful had a son, then I would be the first of [his] worshippers.”
Muhammad Taqi-ud-Din al-Hilali and Muhammad Muhsin Khan,
(43:81) 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].
Mohammed Marmaduke William Pickthall
(43:81) Say (O Muhammad): If the Beneficent One hath a son, then, I shall be first among the worshippers. (But there is no son).
Abdullah Yusuf Ali
(43:81) Say: “If (Allah) Most Gracious had a son, I would be the first to worship.”
Mohammad Habib Shakir
(43:81) Say: If the Beneficent Allah has a son, I am the foremost of those who serve.
Dr. Ghali
(43:81) Say, “In case The All-Merciful has a child, then I am the first among the worshippers.
Ali Unal
(43:81) Say: “If the All-Merciful had a child, I would be the first to worship.”
Amatul Rahman Omar
(43:81) Say, `The Most Gracious (God) has no son and I am the foremost to bear witness to this fact.
Literal
(43:81) Say: “If (there) was to the merciful a child (son), so I am the worshippers` first/beginner .”
Ahmed Ali
(43:81) Say: “If Ar-Rahman had a son I would have been the first of worshippers.”
A. J. Arberry
(43:81) Say: ‘If the All-merciful has a son, then I am the first to serve him.
Abdul Majid Daryabadi
(43:81) Say thou: had the Compassionate a son, shall be the first of his worshippers.
Maulana Mohammad Ali
(43:81)-
Muhammad Sarwar
(43:81) (Muhammad), say, “Had the Beneficent God really had a son, I would certainly have been the first one to worship him.
Hamid Abdul Aziz
(43:81) Say, “If the Beneficent has a son, I am the foremost of those who serve him.”
Faridul Haque
(43:81) Proclaim (O dear Prophet Mohammed – peace and blessings be upon him), If supposedly, the Most Gracious had an offspring* – I would be the first to worship! (*Which is impossible)
Talal Itani
(43:81) Say, If the Most Gracious had a son, I would be the first to worship.
Ahmed Raza Khan
(43:81) Proclaim (O dear Prophet Mohammed peace and blessings be upon him), If supposedly, the Most Gracious had an offspring* I would be the first to worship! (*Which is impossible)
Wahiduddin Khan
(43:81) Say, “If the All Merciful had a son, I would be the first to worship him.”
Safi-ur-Rahman al-Mubarakpuri
(43:81) Say: “If the Most Gracious had a son, then I am the first of the worshippers.”
Ali Quli Qarai
(43:81) Say, If the All-beneficent had offspring, I would have been the first to worship [him].
Hasan al-Fatih Qaribullah and Ahmad Darwish
(43:81) Say (Prophet Muhammad): ‘If the Merciful had a son, I would be the first of the worshipers.
That is translated surah Az Zukhruf ayat 81 (QS 43: 81) in arabic and english text, may be useful.