(1) باب
It was narrated that Ibn Abbas said:
"Allah (SWT) enjoined the prayer on the tongue of your Prophet (ﷺ): four (rak'ahs) while a resident, two rak'ahs while traveling, and one rak'ah during times of fear." (DE)
Reference (DE): Sunan an-Nasa'i 1532 (DE)
In-book reference (DE): Book 18, Hadith 4 (DE)
English translation (DE): Vol. 2, Book 18, Hadith 1533 (DE)