When a Muslim is struck with a calamity, when he loses one of his loved ones, or when he has gone bankrupt, he should be patient and say this statement, the meaning of which is : "We are from Allah and to hom we are returning."
Muslims believe that Allah is the One who gives and it is He takes away. He is testing us. Hence, a Muslim submits himself to Allah. He is grateful and thankful to Allah for whatever he gets. On the other hand, he is patient and says this expression in times of turmoil and calamity.