The Quran

وَوَصَّينَا الإِنسانَ بِوالِدَيهِ إِحسانًا ۖ حَمَلَتهُ أُمُّهُ كُرهًا وَوَضَعَتهُ كُرهًا ۖ وَحَملُهُ وَفِصالُهُ ثَلاثونَ شَهرًا ۚ حَتّىٰ إِذا بَلَغَ أَشُدَّهُ وَبَلَغَ أَربَعينَ سَنَةً قالَ رَبِّ أَوزِعني أَن أَشكُرَ نِعمَتَكَ الَّتي أَنعَمتَ عَلَيَّ وَعَلىٰ والِدَيَّ وَأَن أَعمَلَ صالِحًا تَرضاهُ وَأَصلِح لي في ذُرِّيَّتي ۖ إِنّي تُبتُ إِلَيكَ وَإِنّي مِنَ المُسلِمينَ

Muhammad Asad

NOW [among the best of the deeds which] We have enjoined upon man is goodness towards his parents.¹ In pain did his mother bear him, and in pain did she give him birth; and her bearing him and his utter dependence on her took thirty months.² And so, when he attains to full maturity and reaches forty years,³ he [that is righteous] prays: "O my Sustainer! Inspire me so that I may forever be grateful for those blessings of Thine with which Thou hast graced me and my parents, and that I may do what is right [in a manner] that will meet with Thy goodly acceptance; and grant me righteousness in my offspring [as well]. Verily, unto Thee have I turned in repentance:⁴ for, verily, I am of those who have surrendered themselves unto Thee!"

Cf. 29:8 and 31:14. In the present instance, this connects with the reference to the "doers of good" at the end of verse 12 and in verses 13-14.
See note 14 on 31:14.
I.e., the age at which man is supposed to attain to full intellectual and spiritual maturity. It is to be borne in mind that the masculine noun insan ("man" or "human being") appearing in the first sentence of this verse applies to both sexes alike.
Sc., "of whatever sin I may have cominitted". See note 41 on the last sentence of 24:31.