The treatment of non-bonding valence electron pairs (lone pairs) within molecular orbital theory and localized molecular orbital descriptions is a foundational and uncontroversial topic in chemistry, requiring no special citation.
The claim that lone pairs are explicitly accounted for within molecular orbital theory is a standard textbook fact regarding electronic structure methods (such as molecular orbital theory and NBO analysis). Per instructions, trivially true statements by definition or direct chemical knowledge are classified as COMMON_KNOWLEDGE.