Pranayama, the control of one’s energy or breath, is the fourth limb of Yoga.

Yoga Sutra 2.49 When that exists, control of incoming and outgoing energies is next.
2.50 It may be external, internal, or midway, regulated by time, place, or number, and of brief or long duration.
2.51 Energy-control which goes beyond the sphere of external and internal is the fourth level- the vital.
2.52 In this way, that which covers the light is destroyed.
2.53 Thus the mind becomes fit for concentration.

As with the asanas, it is somewhat difficult to show a direct scriptural basis for the practice.  However, the Bible clearly supports the concept that the breath is a source of power and energy and that this power or energy originates with God.

7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
Genesis 2:7

22 All in whose nostrils was the breath of life . . . .
Genesis 7:22

Simple passages and yet I have a strong feeling that they mean more than simply that Adam started breathing or that all land life breathed air.  These speak more to a power of life that fills us via our breath.  This concept has held my attention since I first read Genesis more than 20 years ago and my study of Yoga has only served to reinforce the concept that breath as a power of life means much more than simple breathing.  I also find it singular that both verses highlight that the breath of life was in their nostrils and that pranayama also stresses breathing through the nostrils.

Namasté