Hasan al-Basri narrated: This narration has reached me that the Prophet (peace and blessings be upon him) said: "When one of you is fasting and forgetfully eats or drinks something, he should complete his fast, for Allah Almighty has fed him and given him to drink."
Imam Ahmad recorded this narration.
This narration is mursal, but it is sahih (authentic) in terms of its chain.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4898
Hadith Gradingمحدثین:إسناده مرسل
Hadith Takhrij«اخرجه احمد فى المسند (493/2) ، أخرجه مسند أحمد برقم: 10020، وأخرجه سنن الدارمي برقم: 1727»