The word(s) "additional" appears 3 time(s) in 3 verse(s) in Quran in Mohsin Khan translation.

(1) And in some parts of the night (also) offer the Salat (prayer) with it (i.e. recite the Qur'an in the prayer), as an additional prayer (Tahajjud optional prayer - Nawafil) for you (O Muhammad صلى الله عليه و سلم). It may be that your Lord will raise you to Maqam Mahmud (a station of praise and glory, i.e. the honour of intercession on the Day of Resurrection.) .

(2) And during a part of the night (also) glorify His praises (i.e. Maghrib and 'Isha prayers) and (so likewise) after the prayers [As-Sunnah, Nawafil - optional and additional prayers. And also glorify, praise and magnify Allah - Subhan Allah, Alhamdu lillah, Allahu-Akbar].

(3) And remembers (glorifies) the Name of his Lord (worships none but Allah), and prays (five compulsory prayers and Nawafil - additional prayers).