Deuteronomy 7:22

Jehovah your God will drive out these nations before you little by little. You will not be able to put an end to them quickly. This is because the wild beasts are too numerous (and will multiply) around you.

Exodus 23:29-30

I will not drive them out within a year's time. If I did, the land would become deserted. There would be too many wild animals for you.

Joshua 15:63

As for the Jebusites the inhabitants of Jerusalem, the children of Judah could not drive them out. The Jebusites dwell with the children of Judah at Jerusalem to this day.

Treasury of Scripture Knowledge

Summary

And the LORD thy God will put out those nations before thee by little and little: thou mayest not consume them at once, lest the beasts of the field increase upon thee.

General references

Bible References

Thou mayest

Exodus 23:29
I will not drive them out within a year's time. If I did, the land would become deserted. There would be too many wild animals for you.
Joshua 15:63
As for the Jebusites the inhabitants of Jerusalem, the children of Judah could not drive them out. The Jebusites dwell with the children of Judah at Jerusalem to this day.

General references

Deuteronomy 11:23
Then Jehovah will drive out all these nations from before you. You will drive out nations greater and mightier than you.
Joshua 21:44
Jehovah granted them peace throughout the land. This is just as he had promised their ancestors. Not one of all their enemies was able to stand against them, because Jehovah gave the Israelites the victory over all their enemies.