The Quran

وَإِذ بَوَّأنا لِإِبراهيمَ مَكانَ البَيتِ أَن لا تُشرِك بي شَيئًا وَطَهِّر بَيتِيَ لِلطّائِفينَ وَالقائِمينَ وَالرُّكَّعِ السُّجودِ

Muhammad Asad

For, when we assigned unto Abraham the site of this Temple,¹ [We said unto him:] "Do not ascribe divinity to aught beside Me!"² - and: "Purify My Temple for those who will walk around it,³ and those who will stand before it [in meditation], and those who will bow down and prostrate themselves [in prayer]."

I.e., the Ka'bah: see note 102 on 2:125.
In view of the oft-repeated Qur'anic statement that Abraham was beyond all temptation to ascribe divinity to anything but God, it seems to me that the above injunction has a specific import, namely, "Do not allow this Temple to become an object of worship, but make it clear that it is holy only by virtue of its being the first temple ever dedicated to the worship of the One God" (cf. 3:96). Apart from that, it refers to "those who are bent on denying the truth" spoken of at the beginning of the preceding verse.
See surah 2, note 104.