Did scholars say that the awrah of a female slave is from navel to knee?

Imam Jassas said: > فيجوز للأجنبي النظر إلى شعر الأمة وذراعها وساقها وصدرها وثديها كما يجوز لذوي المحرم النظر إلى ذات محرمه > > A stranger male can see the hair, arms, legs, chest and breasts of a slave woman just like he can see these parts of his mahram woman > > [\[Imam Jasas, Ahkam al-Qur'an, Dar al-Qutub al-Arabi, Volume - 3\]][2] Is this true? How did he give such a fatwa? Can you do a quick research on this and give an answer?