What is the ruling on Ijtihad in Islam? And what are the conditions for a Mujtahid?

Ijtihad is the exertion of effort to deduce a legal ruling from its legitimate proofs. It is obligatory upon those capable of it, for Allah the Almighty says: (So ask the people of the message if you do not know). The one performing ijtihad must possess vast knowledge of the religious texts, principles, and sayings of scholars, lest he falls into error, like someone who acts upon general hadiths that have been particularized, or abrogated, or contradict the consensus of scholars without him knowing. Thus, the mujtahid must have knowledge of the religious proofs and principles that enable him to extract rulings, and knowledge of what the scholars have agreed upon. Ijtihad can be جزئي (partial), meaning a person can exert effort in a specific issue or a particular branch of knowledge.