(5) باب يَقْصُرُ إِذَا خَرَجَ مِنْ مَوْضِعِهِ
Narrated Anas bin Malik:
offered four rak`at of Zuhr prayer with the Prophet (p.b.u.h) at Medina and two rak`at at Dhul-Hulaifa. (i.e. shortened the `Asr prayer).
Reference: Sahih al-Bukhari 1089
In-book reference: Book 18, Hadith 10
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 20, Hadith 195