And they swear by Allah their strongest oaths that if a sign (6:109)

Almuntakhab Fi Tafsir Alquran Alkarim

The infidels make a solemn declaration with an appeal to Allah that if a significant sign be revealed to them to evince both Muhammad’s Prophethood and integrity; they would most certainly accept it. Say to them: Revelations and signs evincing my Prophethood and the truth of my mission rest in the hands of Allah alone. Nonetheless, how do you know, you Muslims, whether the infidels will or will not favourably respond to the miraculous sign

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(6:109) They swear by Allah with their most solemn oaths that if a sign *74 comes to them, they will certainly believe in it. Say: 'Signs are in Allah's power alone. *75 What will make you realize that even if those signs were to come, they would still not believe? *76

And they swear by Allah their strongest oaths that if a sign meaning

*74). 'Sign' in this context signifies a tangible miracle which is so impressive that it leaves people with no alternative but to believe in the veracity of the Prophet (peace be on him) and the truth of his claim to have been appointed by God.
*75). The Prophet (peace be on him) denies his ability to perform miracles.** That power lies with God alone. If God wants a miracle to take place, He has the power; if He does not want miracles to take place, none will.
**And so indeed does every Prophet of God - Ed.
*76). These words are addressed to the Muslims. Driven by the restless yearning to see people embrace Islam - a yearning which they sometimes expressed in words - they wished some miracle to happen which might lead their erring brethren to the true faith. In response to this wish and longing they are told that their embracing the true faith does not depend upon their observing any miraculous sign.
 

And they swear by Allah their strongest oaths that if a sign meaning in Urdu

یہ لوگ کڑی کڑی قسمیں کھا کھا کر کہتے ہیں کہ اگر کوئی نشانی ہمارے سامنے آ جائے تو ہم اس پر ایمان لے آئیں گے اے محمدؐ! ان سے کہو کہ "نشانیاں تو اللہ کے پاس ہیں" اور تمہیں کیسے سمجھایا جائے کہ اگر نشانیاں آ بھی جائیں تو یہ ایمان لانے والے نہیں