Sunan Ibn Majah, Book 6, Hadith 1576 (In-Book) ⓘ
It was narrated that Abu Hurairah said: “The Prophet said: ‘Offer the (funeral) prayer for your children, for they have gone ahead of you (i.e. to prepare your place in Paradise for you).”
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا الْبَخْتَرِيُّ بْنُ عُبَيْدٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ النَّبِيُّ ـ صلى الله عليه وسلم ـ " صَلُّوا عَلَى أَطْفَالِكُمْ فَإِنَّهُمْ مِنْ أَفْرَاطِكُمْ " .
also referenced under: Hadith 1509 (Reference) & Volume 2, Book 6, Hadith 1509 (DarusSalam)