It is narrated from Hazrat Samurah (may Allah be pleased with him) that once the Prophet (peace and blessings be upon him) said, "By the 'middle prayer' (Salat al-Wusta) is meant the Asr prayer."
Hadith Referenceمسند احمد / أول مسند البصريين / 20129
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، الحسن لم يصرح بسماعه