Mansoor, the Abbasid ruler, invited Imam Jafar e Sadiq (‘a) to Iraq more than often. He was afraid of a revolt initiated by the followers of the Household of the Holy Prophet (s), so he wanted to keep an eye on the Imam(‘a). Often, he would not allow him to return to Medina for days on end.
During one such visit, the commander in chief of the army held a banquet to celebrate the circumcision of his son. All the senior officials of the royal court were invited, including Mansoor, the ruler. The Imam (‘a) was also invited.
The tablecloth was laid and all the guests seated on both sides. Dinner was served. Everyone started eating. A guest asked for water. Instead of water, he was handed a glass of wine. As soon as the Imam (‘a) saw the wine, he got up and left.
While he (‘a) was on his way out, he was urged to return, but he refused saying, ‘The Holy Prophet (s) has said that a person who sits before a tablecloth where wine is being served will invoke the curse of Allah upon himself.’
Reference : Anecdotes of The Ahlul Bayt (Daastaan e Raastaan ) by Ayatullah Murtadha Mutahhari