Answer: Any isosceles triangle is a counter example. More specifically, a triangle with sides 7, 7 and 3
When forming your triangle, make sure you apply the triangle inequality theorem. This is the idea where adding any two sides leads to a result larger than the third side. So we have
7+7 = 14 which is larger than 3
7+3 = 10 which is larger than 7
By definition, an isosceles triangle has two congruent sides. Some books say "at least 2 congruent sides", but I'll go with the first definition. If you want all three sides to be congruent, then you'd go for the term "equilateral".