Patanjali Yoga Sutra 3.12

Sanskrit Sutra

शान्तोदितौ तुल्यप्रत्ययौ चित्तस्यैकाग्रता-परिणामः॥१२॥

Swami Vivekananda's translation

The one-pointedness of the Chitta is when the impression that is past and that which is present are similar.

Chapter link: Yoga Sutra Chapter 3