Making benefits as dowry

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

He said: "I intend to wed one of these my daughters to thee, on condition that thou serve me for eight years; but if thou complete ten years, it will be (grace) from thee. But I intend not to place thee under a difficulty: thou wilt find me, indeed, if Allah wills, one of the righteous."