One verse

Bhagavad Gita 6.6

6.6

बन्धुरात्मात्मनस्तस्य येनात्मैवात्मना जितः | अनात्मनस्तु शत्रुत्वे वर्तेतात्मैव शत्रुवत् ||६-६||

bandhurātmātmanastasya yenātmaivātmanā jitaḥ . anātmanastu śatrutve vartetātmaiva śatruvat ||6-6||

bandhuḥ
friend
ātmā
the mind
ātmanaḥ
of the living entity
tasya
of him
yena
by whom
ātmā
the mind
eva
certainly
ātmanā
by the living entity
jitaḥ
conquered
anātmanaḥ
of one who has failed to control the mind
tu
but
śatrutve
because of enmity
varteta
remains
ātmā eva
the very mind
śatru-vat
as an enemy

For him who has conquered the mind, the mind is the best of friends; but for one who has failed to do so, his mind will remain the greatest enemy.