Reference for Ketubot 108:8

<big><strong>גמ׳</strong></big> פשיטא מהו דתימא קיצותא עבדו רבנן שלא לבייש את מי שאין לו קמ"ל:

Gemara. Is this not obvious? What might you have thought? That the Rabbis set a limit in order not to embarrass someone who does not have funds [to pay for a larger ketubah].

Jastrow