Talmud (Rodkinson Edition) — Book 1…
“ One who tears a thing while in a rage, or through grief, or through mourning for the dead, is culpable, and although he desecrates the Sabbath, the duty of tearing (ordained in cases of mourners for the dead) is fulfilled. This presents no difficulty. The Boraitha treats of the case of a man who tore his garment on account of the death of one on whose account it was his duty to tear his garment, while the Mishna treats of the case of a man who did not do so for duty's sake, but on account of a death of a stranger, and this not being his duty, he merely spoiled his garment. ”
