Imam Jafar al-Sadiq was travelling between Mecca and Medina. Musadaf, his famous serving man, was accompanying him on this journey. On the way, they sighted a man lying under a tree. He seemed in bad shape from a distance. The Imam (‘a) said to Musadaf, ‘Let us go and see what’s wrong with him. It is possible that he has fainted because of thirst and dehydration.’
When they reached him, they found him conscious. The Imam (‘a) asked, ‘Are you thirsty?’ ‘Yes,’ he replied.‘. The Imam (‘a) ordered Musadaf to slake his thirst. He got off his horse and gave the thirsty man enough water to satisfy his thirst. He noticed from his appearance and dress that he was not a Muslim, but a Christian. They resumed their journey. Musadaf asked the Imam (‘a), ‘Can we give alms to Christians?’, ‘Yes, especially when they are in need, as just now.
Reference : Anecdotes of The Ahlul Bayt (Daastaan e Raastaan ) by Ayatullah Murtadha Mutahhari