Sahih Bukhari: Hadith 5133

I (Humaid) said to Zainab, "What does 'throwing a globe of dung when one year had elapsed' mean?" Zainab said, "When a lady was bereaved of her husband, she would live in a wretched small room and put on the worst clothes she had and would not touch any scent till one year had elapsed. Then she would bring an animal, e.g. a donkey, a sheep or a bird and rub her body against it. The animal against which she would rub her body would scarcely survive. Only then she would come out of her room, whereupon she would be given a globe of dung which she would throw away and then she would use the scent she liked or the like."