Al-Hajj: (26) And [mention, O Muhammad], when We designated for Abraham the site of the House...
"And mention when We designated for Abraham the site of the House"
Meaning: A place of return, to which he would return for its maintenance and for worship.
The House was raised to the heavens during the days of the Flood, and it was made of a red ruby. God then indicated its location to Abraham by means of a wind He sent, called al-Khajuj, which swept away everything around it, so he rebuilt it upon its original foundation.
The particle an (in the following verse) is al-mufassirah (explanatory).
If you ask: How can the prohibition of polytheism and the command to purify the House be an explanation for the "designation" (tabu'ah)?
I say: The designation was intended for the purpose of worship. It is as if it were said: "We commanded Abraham to worship, saying to him: 'Do not associate anything with Me, and purify My House' from idols, images, and filth that might be cast around it."
It is also recited as yushrik (in the third person, "that he not associate").
"And proclaim to the people the Hajj [pilgrimage]; they will come to you on foot and on every lean camel; they will come from every deep and distant pass."