Narrated 'Umar (RA):

If anyone acknowledges that he is the father of his child just for the blinking of an eye, he has no right to disown it." [al-Baihaqi reported it. The Hadith is Hasan (good) and Mawquf (saying of a Companion)].

وَعَنْ عُمَرَ ‏- رضى الله عنه ‏- قَالَ: { مَنْ أَقَرَّ بِوَلَدٍ طَرْفَةَ عَيْنٍ, فَلَيْسَ لَهُ أَنْ يَنْفِيَهُ } .‏ أَخْرَجَهُ اَلْبَيْهَقِيُّ, وَهُوَ حَسَنٌ مَوْقُوف ٌ [1]‏ .‏