Assalaamu alaykum. I would like to know what the ruling is on cloth fibres that get under the nails or transfer from the hijab onto the hair. Do they have to be removed before performing ablution? I was wiping my hair one day during ablution, and when I rinsed my hands, I saw the fibres from my hijab in the sink. Thank you!

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

It is understood from the question that these cloth fibers are mere threads, so they do not prevent water from reaching the skin or hair underneath them because they are not stuck to the skin or hair. Hence, you do not have to remove these fibers before performing ablution. As for their presence after ablution, it definitely does not harm.

Allah knows best.