Volunteering is to give time to help others without pay.

志愿活动是无偿地付出时间去帮助别人。

youdao

He would work overtime, without pay, to finish a job.

他会无偿地加班把一件工作完成。

《柯林斯英汉双解大词典》

It was a long and stormy voyage, and they made me work my passage without pay, as a common sailor.

这是一次漫长的暴风雨之旅，他们让我做一名普通的水手，以劳力抵船费。

youdao

But she offered to teach without pay for three months.

VOA: special.2009.07.26

In her first 3 years, Ms. Streeter worked without pay.

VOA: special.2009.01.28

They have fought for you. Without pay or food.

VOA: special.2009.12.17

The 27 staff were suspended for four weeks without pay, for improperly accessing his records.

BBC: NEWS | Entertainment | Clooney hospital punishes staff

For their part, many students say they don't mind working without pay at least, for the moment.

WSJ: Real Work for Future M.B.A.s

Assistant head coach Joe Vitt was suspended without pay for the first six regular-season games.

CNN: Saints head coach expresses 'regret' in bounty scandal