Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Vocative case:

"

The vocative ending changes the stem consonant in Old Church Slavonic because of the so-called First Palatalization. Most[citation needed] modern Slavic languages that retain the vocative case have altered the ending to avoid the change: Bulgarian вълко occurs far more frequently than вълче.