Hadith: Arabic Text followed by English Translation. 

عَنِ ابْنِ مَعْقِلٍ، قَالَ ‏:‏ دَخَلْتُ مَعَ أَبِي عَلَى عَبْدِ اللَّهِ فَسَمِعْتُهُ يَقُولُ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏:‏

النَّدَمُ تَوْبَةٌ فَقَالَ لَهُ أَبِي ‏:‏ أَنْتَ سَمِعْتَ النَّبِيَّ ـ صلى الله عليه وسلم ـ يَقُولُ ‏:‏ ‏”‏ النَّدَمُ تَوْبَةٌ ‏”‏ ‏.‏ قَالَ ‏:‏ نَعَمْ ‏.‏”

رواه إبن ماجه (4252) . وصححه الألباني في صحيح إبن ماجه

It was narrated that Ibn Ma’qil said:
“I entered with my father upon ‘Abdullah, and I heard him say: ‘The messenger of Allah (ﷺ) said:

“Regret is repentance”.My father said: ‘Did you hear the Prophet (ﷺ) say: “Regret is repentance?” He said: ‘Yes.’”

Sunan Ibn Majah, 4252; classed as sahih by al-Albani in Saheeh Ibn Majah.