Yǎn jiàn wèi shí.

眼见为实。

Seeing is believing.

Notes:

眼(yǎn):eye

见(jiàn):to see

为(wéi): is

实(shí): truth

Example:

A：他说他有女朋友了。

     Tā shuō tā yǒu nǚpénɡyǒu le.

     He said he got a girlfriend.

B：眼见为实。

     Yǎn jiàn wèi shí.

     Seeing is believing.