Imaam Ibn Taymiyyah (rahimahullah) was amazed by her knowledge and she knew most of al-Mughni (a book of fiqh which consists of 15 volumes) by heart. Shaykh Ibn Katheer and Shaykh al-Dhahabee have also mentioned her.
She was a fine example and proof that respect for knowledge and those who possessed it was not confined to the formative period of Islaam. Umm Zaynab's knowledge of Jurispudence was respected and admired by her male peers. She learnt Fiqh with Shaykh Shams al Din and other Maqdisi Scholars. (Al Dhahabi, al-Juz’ al-maqfood min Siyaar A’laam al-Nubalaa’, 416)
Shaykh al-Dhahabee also said,
‘A large number of women benefited from her and repented. She had abundance of knowledge, was content with little, keen to benefit people and give sermons with sincerity, God-wariness and for [the sake of] commanding the good. The women of Damascus [and] then [after her fame had spread, and she moved, to Cairo] the women of Egypt were reformed by her. She had a lot of popularity and influence over the hearts [of people].’ (Al-Dhahabi, Dhayl al-‘Ibar, 80; Al-Yafi’I, Mir’aat al-Jinaan, iv. 254. See also al-Dhahabi, al-Juz’ al-mafqood in Siyar a’laam al-nubalaa’, 416.)
Shaykh al-Dhahabee says:
‘I visited her and I liked her character, humility and God-wariness. She knew Fiqh well. Ibn Taymiyyah was amazed by her knowledge and intelligence and praised her fulsomely.’ (Al Dhahabi, al-Juz’ al-maqfood min Siyaar A’laam al-Nubalaa’, 416)
Ibn Katheer says:
‘I heard Shaykh Taqi al-Din ibn Taymiyyah praising her a lot and lauding her virtue and knowledge. he stated that she knew most of al-Mughni by heart. And [he] used to prepare for her many juristic issues [adequetly suited to] her questions and her sharp understanding.’ (Ibn Katheer, al Bidaayah wa al-nihaayah, sub anno 714)
Ibn Katheer also says:
‘She was among the scholars and women of virtue. She commanded good and forbade evil, and opposed the Ahmadiyyah sect for their [illicit] friendshio with women and young boys. And she criticised their states (ahwaal) and the thinking and arguments (usool) of the people of bid’ah (innovation) and others. In [all] that she did what men are unable to do.’ (Ibn Katheer, al Bidaayah wa al-nihaayah, sub anno 714)
Umm Zaynab is known as a reformer of the 7th-8th century – just as Ibn Taymiyyah is revered and praised highly- so is his female contemporary.
She was no less than a great scholar, jurist, ascetic, leader of the women in her time and preacher.
Source: Women Who Taught Their Husbands