Imam Ali (‘a) was hosting a guest for the past many days. The guest had an ulterior motive which he did not reveal until the time was ripe for it. He was actually waiting for the other party to appear so that he could talk about it then. Finding it difficult to restrain himself, one day, he informed Imam Ali (‘a) about the dispute he was engaged in, and that he (‘a) would judge between them.
Imam Ali (‘a) asked him, ‘Are you a member of one of the registered disputing parties?’ ‘Yes.’ ‘Then I’m extremely sorry. I cannot keep you as a guest in my house from this moment onwards, because the Holy Prophet (s) said: “If a judge is presented with a case, he has no right to play host to one party while the other party is not there. Both parties should be treated with the same hospitality, without showing the slightest inclination towards any one of them.”’
Reference : Anecdotes of The Ahlul Bayt (Daastaan e Raastaan ) by Ayatullah Murtadha Mutahhari