the lender remain pledged as security for the remaining debt, or may he revoke the loan at any time?

He replied:

Praise be to Allah. Yes, the debtor may sell his share to discharge his debt, as described. If he sells it and it is subject to the right of pre-emption, his partner may acquire it by exercising that right. As for the lender’s share, it remains pledged as security for the remaining debt, just as before. The lender may not revoke a loan of this kind, because the pledgee’s right is attached to it. And Allah knows best.

He—may Allah have mercy on him—was also asked:

A man had property pledged as security for a sum payable on a specified date. When payment fell due, he paid the creditor what he was owed except for one hundred dirhams. The original document was then torn up, and a written acknowledgment was drawn up for the one hundred dirhams, without mentioning the pledge again. Do these remaining one hundred dirhams retain any claim upon the pledged property?

He replied:

If the debtor pays part of the debt while some remains outstanding, the property remains pledged as security for the outstanding amount, unless something occurs that requires its release, such as the pledgee releasing it, or something similar.