What is it that Allāh has commanded to be joined yet they cut it off?

Imām Ibn al-Jawzī (d. 597 AH / 1201 CE) summarized the scholars' opinions in his book "Zād al-Masīr":

1. The ties of kinship and the rights of relatives. [Ibn ʿAbbās, Qatādah, al-Suddī]
2. The Messenger of Allah, peace be upon him; they cut him off by disbelieving in him. [Al-Ḥasan]
3. The command to believe in Allah and to not differentiate between any of His messengers, yet they believed in some and disbelieved in others. [Muqātil]