Imam al-Shafi'i (may Allah have mercy on him) said: "My view is that regarding the report Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both) narrated of the tahlil of the Prophet (peace and blessings be upon him) (that is, saying La ilaha illallah), and the report Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrated of his (peace and blessings be upon him) takbir (that is, saying Allahu akbar), exactly as these reports have reached us,
I think that he (peace and blessings be upon him) surely recited these words somewhat aloud only so that the people might learn (this remembrance) from him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / Q3013