Sayyiduna Talhah bin Ubaydullah (may Allah be pleased with him) said: I asked the Prophet (peace and blessings be upon him) about the explanation of 'Subhan Allah', and he (peace and blessings be upon him) said: "It is declaring Allah Almighty free from every evil (that is, regarding Him as free from everything that is not befitting His majesty)."
Al-Bazzar recorded it; its chain contains Abd al-Rahman bin Hammad al-Talhi, who is da'if (weak) on account of this narration and others.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16880