vouch for somebody/something phrasal verb ( see also ↑ vouch )
1 . to say that you firmly believe that something is true or good because of your experience or knowledge of it:
I’ll vouch for the quality of the report. I read it last night.
‘Where were you on the night of the murder?’ ‘In bed with flu. My wife can vouch for that.’
2 . to say that you believe that someone will behave well and that you will be responsible for their behaviour, actions etc:
Why don’t you phone my office? They’ll vouch for me.