Visuddhimagga V-25

Itarena succhannamaṇḍape vā cammakaṭasārakādīnaṃ vā aññatarasmiṃ vidatthicaturaṅgulappamāṇaṃ chiddaṃ katvā tadeva vā bhittichiddādibhedaṃ chiddaṃ ‘‘ākāso ākāso’’ti bhāvetabbaṃ.

其它无经验者，则于盖得很密的假屋的壁或任何皮革席子，穿一个（直径）一张手即四指大的孔，仅于那种壁孔等的孔而作「虚空、虚空」（阿迦沙、阿迦沙）的修习。

Ñ(V,25): Anyone else should make a hole a span and four fingers broad in a well-thatched hut, or in a piece of leather, or in a rush mat, and so on. He should develop one of these, or a hole such as a hole in a wall, as 'space, space'.