The phrase "a friend assured" is correct and usable in written English.
It can be used when conveying that a friend has provided reassurance or confidence about something.
Example: "A friend assured me that everything would turn out fine, even though I was feeling anxious about the situation."
Alternatives: "a friend guaranteed" or "a friend promised".
"It's not that people don't like the herring," a friend assured me.
A friend assured me that Yaba is relatively peaceful, but in Nigeria, safety is left to the Almighty.
After she died, a friend assured me that I'd get through the process of "liberating" those little people the same way I got through my mother's harrowing decline.
A friend assured me that the river-forest-ocean hiking combinations around Nature's Valley are even finer than those that had impressed me in the park's eastern reaches.
"I think you're putting too much pressure on yourself," a friend assures Mrs. Shepard.
It happens all the time: when people who are great at interviewing get hired and then can't do the job; when people on American Idol tell the judges how fantastic they are and then can't sing; when a friend assures you he or she can definitely teach you to ski/get you an interview/show you how to use that new app – and then can't.
There was a complete joyful stillness that overwhelmed me, like a hand on my shoulder from a friend, assuring me that everything is all right.
He was finally invited to a party and decided to wear the suit, after a woman friend assured him the guests would be wearing white ties.
Ms. Susman, who turned out to be the cousin of a close friend, assured me that she would never tell anyone what is in my will (or isn't in it) and mentioned the company's privacy policy, under which a tattletale employee risks "termination and other disciplinary measures, up to being criminally prosecuted".
"She's a journalist!" The friend assured me that he had meant it in the best possible way.
A writer-director friend assured me that kids tend to filter out what they don't understand, and I figured that it would be better if I were there to answer the uncomfortable questions.
