The Quran

وَوَصَّينَا الإِنسانَ بِوالِدَيهِ حَمَلَتهُ أُمُّهُ وَهنًا عَلىٰ وَهنٍ وَفِصالُهُ في عامَينِ أَنِ اشكُر لي وَلِوالِدَيكَ إِلَيَّ المَصيرُ

Muhammad Asad

"And [God says:] 'We have enjoined upon man goodness towards his parents: his mother bore him by bearing strain upon strain, and his utter dependence on her lasted two years:¹ [hence, O man,] be grateful towards Me and towards thy parents, [and remember that] with Me is all journeys' end.²

Lit., "his weaning is [or "takes place"] within two years". According to some philologists, the term fisal circumscribes the entire period of conception, gestation, birth and earliest infancy (Taj al-'Arus): in brief, the period of a child's utter dependence on its mother.
Thus, gratitude towards parents, who were instrumental in one's coming to life, is here stipulated as a concomitant to man's gratitude towards God, who is the ultimate cause and source of his existence (cf. 17:23-24).