Sahih Bukhari Volume 002, Book 023, Hadith Number 390.
Narated By Anas bin Malik : We went with Allah's Apostle (p.b.u.h) to the blacksmith Abu Saif, and he was the husband of the wet-nurse of Ibrahim (the son of the Prophet). Allah's Apostle took Ibrahim and kissed him and smelled him and later we entered Abu Saif's house and at that time Ibrahim was in his last breaths, and the eyes of Allah's Apostle (p.b.u.h) started shedding tears. 'Abdur Rahman bin 'Auf said, "O Allah's Apostle, even you are weeping!" He said, "O Ibn 'Auf, this is mercy." Then he wept more and said, "The eyes are shedding tears and the heart is grieved, and we will not say except what pleases our Lord, O Ibrahim ! Indeed we are grieved by your separation."