Jabir acquired a wide knowledge of the Qur'an, Traditions, and Futya. His teacher Ibn 'Abbas was completely satisfied with him. It is reported that Ibn 'Abbas said, "If the people of Basrah turned to the knowledge of Abu al- Sha'tha', he would enrich them with the knowledge of the Book of God." He also described Jabir as one of the learned men, and believed that Jabir had attained such a high standard of knowledge that no-one, even Ibn 'Abbas himself, need be resorted to in order to formulate legal decisions if Jabir had already expressed his opinion. When al-Rabi, a man from Basrah, asked Ibn 'Abbas for his legal decision concerning certain problems, Ibn; Abbas said, "How can you ask us when you have Jabir b. Zaid among you?" Other Companions, viz., 'Abdullah b 'Umar, Jabir b. 'Abdullah al-'Ansari, hold the same opinion of Jabir as Ibn 'Abbas; al-Bukhari reported from Jabir b. Zaid that he said, Ibn 'Umar came across me while I was performing the tawaf (circumambulation of Ka'bah) and said to me, 'Jabir, you are one of the learned men of Basrah, people will come to you asking for fatwas, so do not give any legal decision unless it is clearly stated in the Qur'an or a genuine Sunnah, otherwise you will go astray and lead the people astray." It is also reported that Zaid b. Jubair consulted the Companion Jabir b. 'Abdullah al-'Ansari about a certain case. After he had given his opinion, he said, "Why do you ask me when Abu al- Sha'tha' is among you?" So then Jabir was one of the outstanding learned men of Basrah - according to Muhammad b. Mahbub, Jabir had more knowledge than al-Hasan al-Basri. Jabir became the Mufti of Basrah and spent his life delivering legal opinions, teaching the Traditions of the Prophet, and transmitting his vast knowledge of Islam to his students.
When Jabir died, Anas b. Malik, said: 'The most knowledgeable person on the face of the earth has now died'. Thabit al-Bunani visited Jabir b. Zaid when he was near death and asked him: 'Do you desire anything?' He said: 'I desire to see al-Hasan al-Basri'. Al-Hasan was in hiding out of fear of the tyranny of the Umayyads and their agents. Thabit, knowing his whereabouts, went to al-Hasan and brought him to his dear friend, now on the edge of death the great Muslim Successor spoke to the great Muslim scholar and they exchanged mutual advice in preparation for a long separation in this world and in hope of a happy encounter in the next. Al-Hasan said of his colleague, companion and friend who had departed from this world and met with the next: 'By God, this man was a learned faqih.