We created man from a mingled drop to test him, and We made him hearing and seeing. We guided him on the Way, whether he is thankful or unthankful. (Qur'an, 76:2-3)
We made everything on the earth adornment for it so that We could test them to see whose actions are the best. (Qur'an, 18:7)
Do people imagine that they will be left to say, 'We believe,' and will not be tested? We tested those before them so that Allah would know the truthful and would know the liars. (Qur'an, 29:2-3)
We will test you until We know the true fighters among you and those who are steadfast and test what is reported of you. (Qur'an, 47:31)