How to replicate a specific row (known by its index) N times?

Question

I want to replicate a row N times in a dataframe that I know its index in advance.

For example:

    A   B   C
0   foo 2   3
1   foo 9   nan
2   foo 1   4
3   bar 90  1
4   boo 12  89

Let's say I want to replicate row number 3 three times as follows:

    A   B   C
0   foo 2   3
1   foo 9   nan
2   foo 1   4
3   bar 90  1
4   bar 90  1
5   bar 90  1
6   boo 12  89