The reply given by Sayyidna Ya` qub (علیہ السلام) was: قَالَ سَوْفَ أَسْتَغْفِرُ لَكُمْ رَبِّي shall pray to my Lord to forgive you ... - 98).
Here, Sayyidna Ya` qub (علیہ السلام) has, instead of praying for them instantly, made a promise that he would pray for them soon. Commentators have generally given a reason for this. According to them, his purpose was to pray for them particularly, in peace and with concentration, towards the later part of the night - because the prayer made at that hour is answered specially. This is as it appears in a Hadith in the Sahib of Al-Bukhari and Muslim that, in the last third part of every night, Allah Ta` ala descends in all His Glory close to the firmament near the Earth, and proclaims: Is there someone who would pray to Me, and I would answer? Is there someone who would seek forgiveness from Me, and I would forgive?