Is the 'awrah of a woman in front of other women and her mahrams, from the navel to the knee, proven by evidence?

A woman's 'awrah (intimate parts) in front of other women and her maharim (unmarriageable kin) is the area between the navel and the knee, though there is a difference of opinion regarding the precise definition of this 'awrah. The evidence for this view is what Al-Bayhaqi narrated from Ibn Abbas and Mujahid, and that what appears of her during her work is permissible. As for the husband, he is permitted to look at his wife's 'awrah, and she is permitted to look at his.