"The Salah was enjoined on the lips of the Prophet (ﷺ), four Rak'ahs while resident, and two while traveling, and one Rak'ah during times of fear."
Sunan an-Nasa'i Book 5, Hadith 9
← Previous Hadith "The Salah was enjoined two Rak'ahs at a time, then the Salah when traveling remained like that, but the Salah while resident was increased."

Sunan an-Nasa'i Book 5, Hadith 8 Next Hadith → "How can the Salah be shortened as Allah says: There is no sin on you if you shorten As-Salah (the prayer) if you are in fear?" Ibn 'Umar said: "O son of my brother! The Messenger of Allah (ﷺ) came to us when we had gone astray and he taught us. One of the things that he taught us was that Allah, the Mighty and Sublime, has commanded us to pray two Rak'ahs when traveling."

An-Nisa' 4:101.

Sunan an-Nasa'i Book 5, Hadith 10