Yōga Sūtra 2.38

ब्रह्मचर्यप्रतिष्ठायां वीर्यलाभः।

brahmacaryapratiṣṭhāyāṁ vīryalābhaḥ।

[ब्रह्मचर्य प्रतिष्ठायां वीर्य लाभः।
brahmacarya = continence; pratiṣṭhāyāṁ = when firmly established; vīrya = vigor; lābhaḥ = is the gain;]

When continence (brahmacharya) is firmly established, one gains vigor.