Find the shortest distance between the following pairs of lines:
\[
\mathbf{r_1} = \hat{i} - 4 \hat{j} + 5 \hat{k} + \mu(5 \hat{i} + 9 \hat{j} + \hat{k}), \quad \mathbf{r_2} = 2 \hat{i} + 8 \hat{j} - 6 \hat{k} + \lambda(3 \hat{i} - 2 \hat{j} + \hat{k})
\]