It's a Sahih Muslim Hadith and as per the consensus, there is no Dhaeef Hadith in Sahih Muslim.
(Personally, however, I believe that this Hadith is a fabricated one just like many others)
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَفَّانُ، حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، أَنَّ رَجُلاً، قَالَ يَا رَسُولَ اللَّهِ أَيْنَ أَبِي قَالَ " فِي النَّارِ " . فَلَمَّا قَفَّى دَعَاهُ فَقَالَ " إِنَّ أَبِي وَأَبَاكَ فِي النَّارِ " .
Anas reported: Verily, a person said: Messenger of Allah, where is my father? He said: (He) is in the Fire. When he turned away, he (the Holy Prophet) called him and said: Verily my father and your father are in the Fire.
http://sunnah.com/muslim/1/408
Here is another one from Sahih Muslim:
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَزُهَيْرُ بْنُ حَرْبٍ، قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ عُبَيْدٍ، عَنْ يَزِيدَ بْنِ كَيْسَانَ، عَنْ أَبِي حَازِمٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ زَارَ النَّبِيُّ صلى الله عليه وسلم قَبْرَ أُمِّهِ فَبَكَى وَأَبْكَى مَنْ حَوْلَهُ فَقَالَ " اسْتَأْذَنْتُ رَبِّي فِي أَنْ أَسْتَغْفِرَ لَهَا فَلَمْ يُؤْذَنْ لِي وَاسْتَأْذَنْتُهُ فِي أَنْ أَزُورَ قَبْرَهَا فَأُذِنَ لِي فَزُورُوا الْقُبُورَ فَإِنَّهَا تُذَكِّرُ الْمَوْتَ " .
Abu Huraira reported: The Apostle of Allah (ﷺ) visited the grave of his mother and he wept, and moved others around him to tears, and said: I sought permission from my Lord to beg forgiveness for her but it was not granted to me, and I sought permission to visit her grave and it was granted to me so visit the graves, for that makes you mindful of death
http://sunnah.com/muslim/11/135
