بسم الله الرحمن الرحيم
It is obligatory upon whomsoever performs ablution to ensure that the water reaches all points of his skin and the nails are included in that. Wearing fingernail polish makes the water incapable of reaching every portion of the hand and as a result the obligation of wudhu is incomplete. The Exalted says:
يأيُّها الذين ءامنوا إذا قمتم إلى الصلاة فاغْسلوا وجوهكم و أيديكم إلى المرافق وامْسحوا برءُوسكم و أرجُلكم إلى الكعبين
“O you who believe! Whenever you stand to establish the prayer wash your face and hands to the elbows, and wipe your heads and feet to the ankles.”
If wudhu is incomplete the prayer is invalid and who from the women is pleased with their prayer not being accepted? Thus whoever wears it should remove it when making wudhu.
Translated by Najeeb Al Anjelesi
Source: المنظار في بيان كثير من الأخطاء الشائعة