Musannaf Ibn Abi Shaybah 7474 — Cracking the fingers during prayer

Shu'bah, the freed slave of Ibn Abbas (may Allah be pleased with them both), said: I prayed alongside Sayyiduna Ibn Abbas (may Allah be pleased with them both), and during the prayer I cracked my fingers. When I had completed the prayer, he rebuked me and said: You crack your fingers in prayer?