At the beginning of Acts, the eleven decide that it is appropriate to replace Judas. To do so, they narrow down the list of candidates to two men: Joseph and Matthias. Then they pray, "Show us which of these two you have chosen to take over the apostolic ministry, which Judas left to go where he belongs." After this they cast lots, and it falls to Matthias, so he was added.
There don't seem to be any other examples of praying and then casting lots in the New Testament. Was this practice atypical? And if so, why was the practice adopted for this decision?