When founded shia?

Answer 1

Shia started when prophet many times used the term "shia of Ali" and some times said: "O Ali, you and your shias ..."

for example this is one saying of prophet:

"O Ali, you the first who enters Heaven and your shias are in chairs of light and they are happy and their faces are lumine around me. ask God forgive their mistakes and they will be my neighbors in Heaven.

انت اول داخل الجنة من امتی وان شیعتک علی منابر من نور مسرورون مبیضة وجوههم حولی ,اشفع لهم فیکونون غدا فی الجنة جیرانی

this saying is mentioned in many sunni books like these 2 book:

کفایة الطالب، ص135، و در مجمع الزواید ج 9 ص 131

this is only one example prophet used term "shia of Ali" there are many more cases.