It is narrated from Sufyan bin Abu Zuhair (may Allah be pleased with him), he says that I heard the Messenger of Allah (ﷺ) say: "Whoever keeps a dog, his reward decreases by two qirats every day." The people asked, did you hear this (yourself) from the Messenger of Allah (ﷺ)? He replied, yes! By the Lord of this mosque, (I myself heard it).
Hadith Referenceمسند الإمام الشافعي / كتاب الأطعمة والصيد والذبائح / 1528
Hadith Takhrijاخرجه البخارى الحرث والمزارعة، باب اقتناء الكلب للحرث (2343) ومسلم، المساقاة، باب الأمر بقتل الكلاب ، وبيان نسخه...... الخ (1576)۔