(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." (ES)
Reference (ES): Sunan an-Nasa'i 1532 (ES)
In-book reference (ES): Book 18, Hadith 4 (ES)
English translation (ES): Vol. 2, Book 18, Hadith 1533 (ES)