O son of the King, now I shall speak unto you the mantra which is to be chanted with this process of meditation. One who carefully chants this mantra for seven nights can see the perfect human beings flying in the sky.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
जप्यश्च परमो गुह्यः श्रूयतां मे नृपात्मज । यं सप्तरात्रं प्रपठन् पुमान् पश्यति खेचरान्
japyaśca paramo guhyaḥ śrūyatāṃ me nṛpātmaja | yaṃ saptarātraṃ prapaṭhan pumān paśyati khecarān
SB 4.8.53