Is it permissible to give charity from money given by a husband to a needy sister without his knowledge?

If the husband specifies a particular person or entity to receive his charity (sadaqah), it is not permissible for the wife to give it to anyone else without his permission, because she is his agent. However, if he authorizes her to dispense it to those in need without specifying, then she may give it to any deserving needy person, and her needy relatives, such as her sister and others, are permissible recipients.