Visuddhimagga VIII-170

Evaṃ ayaṃ addhānavasena ittaravasena ca imehākārehi assāsapassāse pajānanto dīghaṃ vā assasanto dīghaṃ assasāmīti pajānāti…pe… rassaṃ vā passasanto rassaṃ passasāmīti pajānātīti veditabbo. Evaṃ pajānato cassa –

如是当知此（瑜伽者）依长时及短时以此等各九种方法而了知于出息入息，「长出息时知我出息长••••••乃至••••••短入息时知我入息短」对于如是了知者：

Ñ(VIII,170): So it should be understood that it is when this bhikkhu knows in-breaths and out-breaths in these nine ways as 'a [long] extent' and as 'a little [duration]' that 'breathing in long, he knows "I breathe in long"; … breathing out short, he knows "I breathe out short" ' is said of him. And when he knows thus:

Dīgho rasso ca assāso,

Passāsopi ca tādiso;

Cattāro vaṇṇā vattanti,

Nāsikaggeva bhikkhunoti. (pārā. aṭṭha. 2.165);

比丘的鼻端，

起了长的和短的

出息与入息，

这样有四种。

Ñ: 'The long kind and the short as well,

The in-breath and the out-breath too,

Such then are the four kinds that happen

At the bhikkhu's nose tip here'.