Tafsir of Az-Zukhruf 43:67

"Friends on that Day will be enemies to one another, except the righteous."

The adverbial phrase [on that Day] is connected to "enemies." The separation [between the noun and the predicate] does not harm the meaning. The intent is that friendships shall be severed on the Day when the Hour comes upon them, and nothing will remain except the friendship of the righteous, who are those who established true friendship for the sake of Allah the Almighty. This is because they shall witness the reward of loving for the sake of Allah the Almighty. The disconnection is deemed significant because it is impossible for a friend—in his capacity as a friend—to become an enemy.

It is said that the meaning is: The friendship of the friends shall be severed on that Day, except for those who avoided evil companions. The difference between the two interpretations is that the "righteous" in the first view is the one who loved his companion for the sake of Allah the Almighty, and thus guarded [the state of] love from being tainted by any non-divine motive; whereas in the second view, he is the one who guarded himself against the company of the wicked.

In both interpretations, the exception is muttasil (connected). It is also permitted that [on that Day] be connected to "friends," with the intent being the friends in this world, and that the connection to "enemies" is implied, meaning: "enemies in the Hereafter." It is said that the verse was revealed concerning Ubayy ibn Khalaf and Uqbah ibn Abi Mu'ayt.