In the beginning of the Treta-yuga the sun-god instructed devotional service to Manu, and Manu in his turn instructed it to Iksvaku for the welfare of the whole human society

Expressions researched:
"In the beginning of the Tretā-yuga the sun-god instructed devotional service to Manu, and Manu in his turn instructed it to Ikṣvāku for the welfare of the whole human society"

Srimad-Bhagavatam

SB Canto 1

The Lord's incarnation Matsya (the gigantic fish) was advented during the beginning of Vaivasvata Manu's reign. He learned the principles of Bhagavad-gītā from his father, Vivasvān, the sun-god, and he reinstructed the same to his son Mahārāja Ikṣvāku. In the beginning of the Tretā-yuga the sun-god instructed devotional service to Manu, and Manu in his turn instructed it to Ikṣvāku for the welfare of the whole human society.

SB 1.12.19, Translation and Purport

The learned brāhmaṇas said: O son of Pṛthā, this child shall be exactly like King Ikṣvāku, son of Manu, in maintaining all those who are born. And as for following the brahminical principles, especially in being true to his promise, he shall be exactly like Rāma, the Personality of Godhead, the son of Mahārāja Daśaratha.

The Manu mentioned in this verse as the father of Ikṣvāku is the seventh Manu, of the name Vaivasvata Manu, the son of sun-god Vivasvān, to whom Lord Kṛṣṇa instructed the teachings of Bhagavad-gītā prior to His teaching them to Arjuna. Mankind is the descendant of Manu. This Vaivasvata Manu had ten sons, named Ikṣvāku, Nabhaga, Dhṛṣṭa, Śaryāti, Nariṣyanta, Nābhāga, Diṣṭa, Karūṣa, Pṛṣadhra and Vasumān. The Lord's incarnation Matsya (the gigantic fish) was advented during the beginning of Vaivasvata Manu's reign. He learned the principles of Bhagavad-gītā from his father, Vivasvān, the sun-god, and he reinstructed the same to his son Mahārāja Ikṣvāku. In the beginning of the Tretā-yuga the sun-god instructed devotional service to Manu, and Manu in his turn instructed it to Ikṣvāku for the welfare of the whole human society.