Yōga Sūtra 2.06

दृग्दर्शनशक्त्योरेकात्मतेवास्मिता।

dr̥gdarśanaśaktyōrēkātmatēvāsmitā।

[दृक् दर्शन शक्त्योः एकात्मत एव अस्मिता।
dr̥k = act of observing; darśana = the perceived seen; śaktyōḥ = person observing; ēkātmata = one single self; ēva = as if; asmitā = ego;]

Ego (asmita) unites the act of observing, the perceived seen, and the person observing - as if one single self.

It is ego which unites all activities of senses, mind, and the experiences so generated to give the impression of one single self.