Sayyiduna Abu Rafi' (may Allah be pleased with him) says that when Sayyidah Fatimah (may Allah be pleased with her) gave birth to Sayyiduna Hasan (may Allah be pleased with him), she said to the Messenger of Allah (peace and blessings be upon him): Shall I not shed blood on behalf of my son? He (peace and blessings be upon him) said: "No, but shave his hair and give silver equal to the weight of his hair in charity to the awfad or to the poor." Sharik (may Allah have mercy on him) said: By the awfad he meant the people of the Suffah. So she did that, and when Sayyiduna Husayn (may Allah be pleased with him) was born, Sayyidah Fatimah (may Allah be pleased with her) did the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19299