Melachim Bais 11:2

2 But Yehosheva Bat HaMelech Yoram, achot Achazyahu, took Yoash ben Achazyahu, and stole him from among the Bnei HaMelech which were being slain; and they hid him, even him and his nurse, in the cheder hamittot (bedroom) from Atalyah, so that he was not slain.