It is disliked to count with the hand, whether with the fingers or with a thread held; because it is not part of the prayer and contradicts humility. However, counting with the fingertips and memorizing in the heart is not disliked by consensus, and counting with the tongue invalidates the prayer by consensus. See: Nuzhat al-Fikr in Subhat al-Dhikr, pp. 65-75.