Al-Adab Al-Mufrad, Book 8, Hadith 154 (English) ⓘ

He said that the Messenger of Allah, may Allah bless him and grant him peace, said, "Who do you reckon to be the childless among you?" They said, "They are those who do not have any children." No," he said, "The childless are those who have not sent any of their children ahead (i.e. none of their children have died)."

قَالَ‏:‏ وَقَالَ رَسُولُ اللهِ صلى الله عليه وسلم‏:‏ مَا تَعُدُّونَ فِيكُمُ الرَّقُوبَ‏؟‏ قَالُوا‏:‏ الرَّقُوبُ الَّذِي لاَ يُولَدُ لَهُ، قَالَ‏:‏ لاَ، وَلَكِنَّ الرَّقُوبَ الَّذِي لَمْ يُقَدِّمْ مِنْ وَلَدِهِ شَيْئًا‏.‏