Wǒ xiān shuì le.
我先睡了。
I'm heading to bed.
Notes:
我(wǒ): I
先(xiān): first
睡(shuì): to sleep
了(le): particle word
Example:
A:我先睡了。
Wǒ xiān shuì le.
I'm heading to bed.
B:晚安。
Wǎn ān.
Good night.