Sayyiduna Abu al-Darda' (may Allah be pleased with him) reports this saying of the Prophet (peace and blessings be upon him): "We have been commanded with this glorification: that after the prayers 'Subhan Allah' be recited 33 times, 'Al-hamdu lillah' 33 times and 'Allahu akbar' 34 times."
Al-Tabarani recorded it with two chains, and the narrators of both are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16914