Sayyed Muhammad Husaini Ragheb, Sayyed Muhammad Husaini Ragheb has a BA in Law from Guilan University, Iran and has also undertaken Hawzah studies in Qom. He is a Cultural Affairs director of Ethics Group of Al-Mustafa Open... Answer updated 10 months ago

The number is not mentioned, but in fact, if it's like a bunch of hair then prayer in these clothes should be avoided.
see:
Question: Does cat hair affect ones prayers?
Answer: If there is a few cat hairs (one to three) on a person's body or cloth, his prayer is in order but if there are more than that, his prayer becomes void, as an obligatory precaution.

https://www.sistani.org/english/qa/01130/

see also:
https://www.islamquest.net/en/archive/question/fa745