In the Holy Qur'an

Be sure we shall test you with something of fear and hunger, some loss in goods or lives or the fruits (of your toil), but give glad tidings to those who patiently persevere (2:155)

In the Traditions

The Prophet said, "When Allah loves a servant He tests him with tribulations, and if he endures these He selects him (from His Proximity), and if he bears them iwth satisfcation, He distinguishes him (a higher status)."