One day Yao-shan Wei-yen (750-834), one of the well-known Chinese Ch'an master, was asked by the host of the monastery to give his sermon to the assembly who for a long while was expecting his teaching. Yao-shan said: "Strike the bell."
ZAZEN MEDITATION GUIDE - Chapter 4. Cushions and Pads
Cushions and Pad You will need a cushion and a pad in sitting zazen. The pad is about 28 inches square, stuff with kapok or cotton batting so it will be about 1.5 inches thick. The cushion which is stuffed kapok or cotton batting, too, and about 12 - 18 inches in diameter and it flattens out like a pillow to set upon the pad. You may use a pillow if you wish.