Sunan Ibn Majah 1075
سنن ابن ماجه#1075SahihIt was narrated that Ibn ‘Abbas said:“The Messenger of Allah (ﷺ) stayed for nineteen days in which he shortened his prayer to two Rak’ah. So, whenever we stayed for nineteen days we would shorten our prayer to two Rak’ah, but if we stayed more than that we would pray four Rak’ah.”
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Bukhari
In-book reference: 5:273