"Asana having been perfected, the suspension of both the process of drawing in of external air and the exhalation of internal air constitutes pranayama (1)". (Vyasa)
"(1) The pranayama mentioned in this yoga is not the same as those mentioned in Hatha Yoga as exhalation (Rechaka), inhalation (Puraka) and suspension (Kumbhaka).
Some commentators have tried to make the two correspond but that is not proper.
If the air is not expelled after inhalation, there is a cessation of the movement of breath; this is one pranayama. Similarly if after explosion of air, the movement of the breath is suspended that also is a pranayama. Thus has the pranayama to be practiced one after another. A description of the Pranayama as suspension after exhalation has been given in Sutra I-35 (actually I-34).
Pranayama can be performed after Asana has been perfected.
When Asana has not been wholly perfected, Pranayama can be practiced only when during Asana the body becomes steady and the mind is occupied with a sense of void, or any other form of steadiness is established.
Pranayama practiced with a restless mind cannot be regarded as a part of yoga.
Just as in every Pranayama, the movement of the ingoing and outgoing breath is suspended, even so unless steadiness of the body and concentration of the mind on one subject are maintained it does not become pranayama conducive to Samadhi.
That is why the practice of concentration of mind along with the practice of Asana is necessaryy from the beginning.
Concentrating the mind either on God, or on a feeling of physical or mental void, or on a feeling of luminosity within the heart, the synchronisation of each ingoing and outgoing breath with the object of concentration has to be practiced.
That is, the object of concentration should be present in the mind during each act of inhalation and exhalation, or the inhalation and exhalation are to be looked upon as the predisposing causes bringing the thought of the object of concentration; thus union between the breath and the object of concentration has to be practiced.
When this becomes habitual, then the suspension of the movement (of breath) has to be practiced.
During this practice, the mind has also to be kept fixed on the object of concentration. that is the suspension of breath and the mind’s fixation on the objects of concentration should be made as a single effort, or the idea has to be entertained that by the suspension of the breath the object of meditation itself has been held tightly in mental embrace.
This form of suspension of movement of the mind, as long as the suspension of the breath is maintained, indicates one real pranayama.
Dharana (fixation of the mind on an object) has to be practiced with the help of this form of pranayama performed successively.
In Samadhi, however, the breath becomes first delicate then imperceptible , or is even wholly suspended.
The purport of this aphorism is "The suspension of both the internal movement of air in the form of inhalation and external movement in the form of exhalation, is pranayama. in how many ways, the suspension can be practiced will be shown in the next aphorism".
The Philosophy of Patanjali - Swami Hariharananda Aranya.
In commentary above Aranya makes reference to sutra 1-35 ( he actually means 1-34 ), here it is...