What is the authority that generally releases obligations, contracts, and quasi-contracts?

Among the most important references on obligations and contracts are: Al-Mughni by Ibn Qudamah, Al-Majmoo' by Al-Nawawi, Al-Mabsoot by Al-Sarakhsi, Hashiyat al-Dussuqi, Al-Hattab, Al-Mawsu'ah Al-Kuwaitiyah (The Kuwaiti Encyclopedia of Fiqh), Fiqh Al-Sunnah by Sayyid Sabiq, Al-Fiqh Al-Islami wa Adillatuh (Islamic Jurisprudence and its Proofs) by Wahbah Al-Zuhayli, Ilzamat Al-Hattab, Al-Tabsira by Ibn Farhun, Al-Bahjah by Al-Tasouli, Al-Milkiyah wa Nazariyat Al-'Aqd (Ownership and Contract Theory) by Abu Zahra, and Mabda' Al-Rida fi Al-'Uqud (The Principle of Consent in Contracts) by Dr. Ali Muhyi Al-Din Al-Qarah Daghi.