Is there a relationship between the four schools of thought, and in what situation is it permissible for one school of thought to benefit from another?

There is a close relationship between the four schools of thought (madhahib) due to their agreement on many fundamental principles such as the the Qur’an, the Sunnah, consensus (ijma‘), and analogical reasoning (qiyas). Personal relationships also existed between the imams. For example, Al-Shafi‘i was a student of Malik, and Ahmad was a student of Al-Shafi‘i. Furthermore, Muhammad ibn al-Hasan al-Shaybani and Abu Yusuf were students of Malik. It is permissible for a Muslim who adheres to one madhhab to adopt the opinion of another imam in matters of ijtihad (independent juristic reasoning), provided that it is not for the purpose of seeking out dispensations (rukhus). The Companions unanimously agreed on the permissibility of this.