Maliks Muwatta Book 1, Hadith Number 22.
Section : The Times of Prayer in General.
Yahya related to me from Malik from Yahya ibn Said that once Umar ibn al-Khattab left after doing the asr prayer and met a man who had not been there. Umar asked him what had kept him from the prayer and even though the man gave a good reason, Umar said, “You have given yourself short measure.”
Yahya added that Malik commented, “It is said that everything has a short measure and a full measure.”