Anas ibn Malik reported: The Messenger of Allah, peace and blessings be upon him, said when the month of Ramadan began, “Verily, this month has presented itself to you. There is a night within it that is better than a thousand months. Whoever is deprived of it has been deprived of all good, and none is deprived of its good but that he is truly deprived.”
Source: Sunan Ibn Mājah 1644
Grade: Hasan (fair) according to Al-Albani
عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ دَخَلَ رَمَضَانُ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّ هَذَا الشَّهْرَ قَدْ حَضَرَكُمْ وَفِيهِ لَيْلَةٌ خَيْرٌ مِنْ أَلْفِ شَهْرٍ مَنْ حُرِمَهَا فَقَدْ حُرِمَ الْخَيْرَ كُلَّهُ وَلَا يُحْرَمُ خَيْرَهَا إِلَّا مَحْرُومٌ
1644 سنن ابن ماجه كتاب الصيام باب ما جاء في فضل شهر رمضان
2247 المحدث الألباني خلاصة حكم المحدث حسن في صحيح الجامع