zhè / jiàn / shì / kǒu / shuō / wú / píng / wǒ / men / hái / shì / bǎ / yuē / dìng / xiě / xià / lái / ba

这件事口说无凭，我们还是把约定写下来吧。

Words alone are not enough for this matter, so let's put the agreement in writing.