vouch for (someone or something)
1. To state one's personal confidence in someone or something as reliable, effective, etc.; to personally guarantee someone or something. I can't believe you fell asleep on the job even after I vouched for you! I drove one of these for 20 years, so I can definitely vouch for its dependability.
2. To act as evidence supporting something. Your long list of published works certainly vouches for your expertise in the field.
vouch for someone or something
to support or back someone or something; to endorse someone or something. I can vouch for Tom. Irene will vouch for my honesty.
vouch for
v.1. To give personal assurances of something or someone; give a guarantee of something or someone: I can't vouch for that company's reliability because I've never dealt with them.
2. To constitute supporting evidence for something; give substantiation for something: The candidate's strong record vouches for her ability.