The word(s) "foundation" appears 6 time(s) in 5 verse(s) in Quran in Mohsin Khan translation.

(1) And (remember) when Ibrahim (Abraham) and (his son) Isma'il (Ishmael) were raising the foundations of the House (the Ka'bah at Makkah), (saying), "Our Lord! Accept (this service) from us. Verily! You are the All-Hearer, the All-Knower."

(2) It is He Who has sent down to you (Muhammad صلى الله عليه وسلم) the Book (this Qur'an). In it are Verses that are entirely clear, they are the foundations of the Book [and those are the Verses of Al-Ahkam (commandments), Al-Fara'id (obligatory duties) and Al-Hudud (legal laws for the punishment of thieves, adulterers)]; and others not entirely clear. So as for those in whose hearts there is a deviation (from the truth) they follow that which is not entirely clear thereof, seeking Al-Fitnah (polytheism and trials), and seeking for its hidden meanings, but none knows its hidden meanings save Allah. And those who are firmly grounded in knowledge say: "We believe in it; the whole of it (clear and unclear Verses) are from our Lord." And none receive admonition except men of understanding. (Tafsir At-Tabari).

(3) Never stand you therein. Verily, the mosque whose foundation was laid from the first day on piety is more worthy that you stand therein (to pray). In it are men who love to clean and to purify themselves. And Allah loves those who make themselves clean and pure [i.e. who clean their private parts with dust (which has the properties of soap) and water from urine and stools, after answering the call of nature].

(4) Is it then he who laid the foundation of his building on piety to Allah and His Good Pleasure better, or he who laid the foundation of his building on the brink of an undetermined precipice ready to crumble down, so that it crumbled to pieces with him into the Fire of Hell. And Allah guides not the people who are the Zalimun (cruel, violent, proud, polytheist and wrong-doer).

(5) Those before them indeed plotted, but Allah struck at the foundation of their building, and then the roof fell down upon them, from above them, and the torment overtook them from directions they did not perceive.