Answer:
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
Assalamu ‘alaykum wa rahmatullahi wa barakatuhu,
If a halal mortgage provider stipulates in the purchase agreement that, if a client repays more than 10% above the yearly repayment amount, they must pay an “early repayment fee,” then such a fee is not jaa’iz. One is still permitted to repay early despite the fee being stipulated, and the stipulation itself is deemed null and batil.
Imposing a fee solely due to early repayment amounts to a financial penalty for a lawful act. Such a condition is neither valid nor enforceable in Shariah. In fact, it is oppressive.
The Prophet ﷺ said:
لاَ ضَرَرَ وَلاَ ضِرَارَ
“There should be neither harm nor reciprocating harm.”–Sunan Ibn Majah, Hadith #2341.
And he ﷺ also said:
وَالْمُسْلِمُونَ عَلَى شُرُوطِهِمْ إِلاَّ شَرْطًا حَرَّمَ حَلاَلاً أَوْ أَحَلَّ حَرَامًا
“The Muslims are bound by their conditions, except a condition that makes the lawful unlawful or the unlawful lawful.”—Sunan al-Tirmidhi, Hadith #1352
Hence, considering the above, one is permitted to repay early without an amount restriction, and a penalty fee for excessive repayment is not jaa’iz.
And Allah ﷻ knows best.
فإن كان صوابا فمن الله وإن كان خطأ فمني ومن الشيطان والله ورسوله بريئان منه