The Quran

فَلَعَلَّكَ تارِكٌ بَعضَ ما يوحىٰ إِلَيكَ وَضائِقٌ بِهِ صَدرُكَ أَن يَقولوا لَولا أُنزِلَ عَلَيهِ كَنزٌ أَو جاءَ مَعَهُ مَلَكٌ ۚ إِنَّما أَنتَ نَذيرٌ ۚ وَاللَّهُ عَلىٰ كُلِّ شَيءٍ وَكيلٌ

Muhammad Asad

IS IT, then, conceivable [O Prophet] that thou couldst omit any part of what is being revealed unto thee [because the deniers of the truth dislike it,- and] because thy heart is distressed at their saying,¹ "Why has not a treasure been bestowed upon him from on high?" - or, "[Why has not] an angel come [visibly] with him?"² [They fail to understand that] thou art only a warner, whereas God has everything in His care;³

Lit., "because thy bosom is constricted [for fear] lest they say". According to all available authorities, the expression la'alla (lit., "it may well be that") at the beginning of the above sentence denotes a wrong expectation on the part of the opponents of Muhammad's message; it is, therefore, best rendered in the form of a query which implies its own denial - thus: "Is it conceivable that...", etc. As regards the expectation that the Prophet might omit a part of what was being revealed to him, it has been reported by 'Abd Allah ibn 'Abbas and other Companions ( see Razi's commentary on this verse) that the pagan Quraysh demanded of the Prophet, "Bring us a revelation (kitab) which does not contain a defamation of our deities, so that we could follow thee and believe in thee."
Explaining this verse, Ibn 'Abbas mentions that some of the pagan chieftains of Mecca said, "O Muhammad, cause the mountains of Mecca to be turned into gold, if thou art truly an apostle of God", while others exclaimed derisively, "Bring before us angels who would bear witness to thy being a prophet!" - whereupon the above verse was revealed (Razi). Cf. 6:8 and 17:90-93.
Sc., "and so it is He who will cause the truth to prevail". Regarding the Prophet's denial of any ability on his part to perform miracles, see 6:50 and the corresponding note 38.