You will have to edit faenza index.theme.

You can find it in Faenza icon folder, e.g. /usr/share/icons/Faenza.

Open it as root

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sudo gedit /usr/share/icons/Faenza/index.theme

Locate 3th line from the top. It should look like that

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Inherits=Faience

Change it to

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Inherits=Faience,ubuntu-mono-light

Restart your theme with unity-tweak-tools or just log out.