What is the ruling on crying and mourning for a deceased person?

Crying for a deceased person is an expression of the mercy that Allah has bestowed upon human beings. The Prophet Muhammad (peace be upon him) also wept when his son Ibrahim died, and when he was informed that his grandchild was about to die, tears flowed from his eyes. When asked about the reason, he said, “This is mercy which Allah has placed in the hearts of His servants. Allah shows mercy only to those of His servants who are merciful.” (Bukhari, Janaiz, 43 [1303]; Muslim, Janaiz, 11,12 [923, 924]; Abu Dawud, Janaiz, 28 [3125]). However, it is not permissible for those left behind to wail loudly, tear their clothes, or engage in excessive lamentation after a death. The Prophet (peace be upon him) said, “Whoever tears his collar, slaps his face and cheeks, and calls to the ways of ignorance when afflicted by a calamity is not one of us.” (Abu Dawud, Janaiz, 29 [3128]); “May Allah keep far from His mercy the woman/person who slaps her face with her hands, scratches her face, tears her collar, and prays for her own destruction and calamity.” (Ibn Majah, Janaiz, 52 [1584]).

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu