What is the ruling on using the expressions "qab qawsayn aw adna" (the distance of two bow-lengths or nearer) and "nun wa ma ya'lamun" (Nun, and what they know not) in casual speech, without intending mockery?

Scholars call this usage of verses "tamaththul" (figurative use) or "iqtibas" (quotation), which is incorporating the Quran into speech without claiming it is part of it. It is permissible to use the phrase "qaba qawsayn aw adna" (the space of two bow-lengths or nearer) in an appropriate context to enhance speech and meaning, and not for mockery or idle talk.

As for the phrase "Today we saw Nun," if it refers to the verse "Nun. By the pen and what they inscribe," then what has been stated above applies to it.

Ibn Uthaymeen was asked about using verses and Sunnah in jest, and he replied that whoever uses them for mockery and ridicule may exit Islam, because it is not permissible to mock the Quran and religious rulings. However, citing a verse to a real-life event is permissible, as the Prophet (peace be upon him) did it. But applying verses to meanings other than what Allah intended, especially with mockery, is a very serious matter.