وَوَهَبْنَا لَهُ إِسْحَقَ وَيَعْقُوبَ نَافِلَةً
...
And We bestowed upon him Ishaq, and Ya`qub Nafilatan.
Ata' and Mujahid said,
"Nafilatan means as a gift."
Ibn Abbas, Qatadah and Al-Hakam bin `]Uyaynah said,
"The gift of a son who has a son,"
meaning that Yaqub was the son of Ishaq, as Allah says:
فَبَشَّرْنَـهَا بِإِسْحَـقَ وَمِن وَرَاءِ إِسْحَـقَ يَعْقُوبَ
But We gave her glad tidings of Ishaq, and after Ishaq, of Yaqub. (11:71)
Abdur-Rahman bin Zayd bin Aslam said,
"He asked for one (son), and said,
رَبِّ هَبْ لِى مِنَ الصَّـلِحِينِ
"My Lord! Grant me from the righteous." (37:100)
So Allah gave him Ishaq, and gave him Yaqub in addition.
...
وَكُلًّ جَعَلْنَا صَالِحِينَ
Each one We made righteous.
means, both of them were good and righteous people.