Bhagavad Gita 2.32

Blessed are the soldiers who find their opportunity; this opportunity has opened for thee the gates of heaven.

यदृच्छया चोपपन्नं स्वर्गद्वारमपावृतम्।
सुखिनः क्षत्रियाः पार्थ लभन्ते युद्धमीदृशम्॥

yadṛcchayā copapannaṃ svargadvāramapāvṛtam|
sukhinaḥ kṣatriyāḥ pārtha labhante yuddhamīdṛśam||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).