Hasan al-Basri (may Allah have mercy on him) narrates that Sayyiduna Samurah (may Allah be pleased with him) said: "I remember two pauses in prayer: the first pause from when the imam says the takbir until he begins the recitation, and the second pause when the imam finishes reciting Surah al-Fatihah and another surah."
The narrator says that Sayyiduna Imran bin Husayn (may Allah be pleased with him) denied this. Then they wrote a letter about this matter and sent it to Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) in Madinah, and he confirmed what Sayyiduna Samurah (may Allah be pleased with him) had said.
A report is transmitted from Hushaym, via Yunus, that when he (peace and blessings be upon him) recited "nor of those who go astray" [Surah al-Fatihah: 7], he "fell silent for a while." He did not mention the surah.
Humayd al-Tawil narrates via al-Hasan: "He (peace and blessings be upon him) would make one pause when he finished the recitation."
Ash'ath reports from al-Hasan: "When he (peace and blessings be upon him) finished the recitation, he would pause."
Here there is also the possibility that this explanation came from those who narrated from al-Hasan. That is why they differ among themselves, and there is evidence for this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3078