Assalaamu alaykum. Is snapping one's finger haram? Can we do it while singing nasheeds?

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. 

Snapping the fingers is known in the Arabic language as Tafqee’. Lisaan-ul-‘Arab reads, “Tafqee’: the sound of snapping or cracking the fingers. Ibn ‘Abbaas, may Allah be pleased with him, reported that the Prophet, sallallahu ‘alayhi wa sallam, forbade Tafqee’ during the prayer. It is also known as Farqa‘ah (popping).”

The basic principle is that snapping the fingers – outside the prayer – is permissible, and there is no evidence forbidding it, whether while singing Nasheeds or otherwise.

Allah knows best.