Money that is received from interest is Haraam in Islaam. That money must be given back to the owner. Allah says in the Quraan in Ayah 275 of Surah Baqarah:
وَأَحَلَّ اللََُّّ الْبَيْعَ وَحَرَّمَ ال رِ ب
Allah Ta'aala has permitted trade and has forbidden interest.
