in a month of Sundays

not in a month of Sundays

if you say that something will not happen in a month of Sundays, you mean that it is not likely to happen He'll never run the marathon, not in a month of Sundays.
See also: month, of, Sundays
References in classic literature ?
I ain't seen so many black eyes and bloody noses in a month of Sundays.
What it was doesn't much matter, but no outsider would have found those keys in a month of Sundays.