After these things the word of the LORD came to Abram in a vision: “Fear not, Abram, I am your shield; your reward shall be very great.” But Abram said, “O LORD God, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?” And Abram said, “Behold, you have given me no offspring, and a member of my household will be my heir.” And behold, the word of the LORD came to him: “This man shall not be your heir; your very own son shall be your heir.” And he brought him outside and said, “Look toward heaven, and number the stars, if you are able to number them.” Then he said to him, “So shall your offspring be.” And he believed the LORD, and he counted it to him as righteousness…

Then the LORD said to Abram, “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for four hundred years. But I will bring judgment on the nation that they serve, and afterward they shall come out with great possessions” …

When the sun had gone down and it was dark, behold, a smoking fire pot and a flaming torch passed between these pieces. On that day the LORD made a covenant with Abram, saying, “To your offspring I give this land, from the river of Egypt to the great river, the river Euphrates, the land of the Kenites, the Kenizzites, the Kadmonites, the Hittites, the Perizzites, the Rephaim, the Amorites, the Canaanites, the Girgashites and the Jebusites.”

via Genesis 15 – ESVBible.org.

So one is justified when one trust God, and God’s promise is to vindicate his people after allowing them to be oppressed.

Notice that Habakkuk ends with a similar statement of faith:

I hear, and my body trembles;
my lips quiver at the sound;
rottenness enters into my bones;
my legs tremble beneath me.

Yet I will quietly wait for the day of trouble
to come upon people who invade us.

Though the fig tree should not blossom,
nor fruit be on the vines,
the produce of the olive fail
and the fields yield no food,
the flock be cut off from the fold
and there be no herd in the stalls,
yet I will rejoice in the LORD;
I will take joy in the God of my salvation.
God, the Lord, is my strength;
he makes my feet like the deer’s;
he makes me tread on my high places.

Thus, Habbakuk also states who is counted righteous before God:

Behold, his soul is puffed up; it is not upright within him,
but the righteous shall live by his faith.