Muwatta Malik · Hadith 1450

وَحَدَّثَنِي مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ وَهُوَ مُسْنِدٌ ظَهْرَهُ إِلَى الْكَعْبَةِ مَنْ أَخَذَ ضَالَّةً فَهُوَ ضَالٌّ ‏.‏

Malik related to me from Yahya ibn Said from Said ibn al-Musayyab that Umar ibn al-Khattab said while he was leaning his back against the Kaba, "Whoever takes a stray is astray

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).