Tafsir of Ash-Shu`ara' 26:123

{كَذَّبَتْ عَادٌ الْمُرْسَلِينَ}

The feminine gender of the verb here is used because what is intended by 'Ad' is the tribe, which is the name of their most distant ancestor. It is very common to refer to a tribe by the name of the ancestor when it is a great one. It may also be referred to by the word 'Banu' (sons of) or 'Al' (family of) appended to it, such as saying: "Banu so-and-so" or "Al so-and-so." The same applies to the words of the Glorified: [...]