﴿ قَالَ إِنِّىٓ أُرِيدُ أَنْ أُنكِحَكَ إِحْدَى ٱبْنَتَىَّ هَٰتَيْنِ عَلَىٰٓ أَن تَأْجُرَنِى ثَمَٰنِىَ حِجَجٍۢ ۖ فَإِنْ أَتْمَمْتَ عَشْرًۭا فَمِنْ عِندِكَ ۖ وَمَآ أُرِيدُ أَنْ أَشُقَّ عَلَيْكَ ۚ سَتَجِدُنِىٓ إِن شَآءَ ٱللَّهُ مِنَ ٱلصَّٰلِحِينَ ﴾

“[After some time, the father] said: “Behold, I am willing to let thee wed one of these two daughters of mine on the understanding that thou wilt remain eight years in my service; and if thou shouldst com­plete ten [years], that would be [an act of grace] from thee, for I do not want to impose any hardship on thee: [on the contrary,] thou wilt find me, if God so wills, righteous in all my dealings.””

Please check ayah 28:28 for complete tafsir.