Patanjali's yoga sutras

संस्कारसाक्षात्करणात्पूर्वजातिज्ञानम् ॥ ३.१८॥

3.18 samskārasāksātkaranāt pūrvajātijñānam

samskara = personality traits accumulated from past experiences

saksatkaranat = direct perception

pūrvajāti = past incarnations

jnanam = insight

Through direct perception of your samskaras, you will gain insight into your past incarnations.