I am the most knowledgeable of people, or among the most knowledgeable, regarding the time of the Messenger of Allah's ﷺ Isha prayer. He used to pray it after the moon had set on the third night from the beginning of the month.
حدثنا هشيم أخبرنا أبو بشر عن حبيب بن سالم
أنا أعلم الناس أو كأعلم الناس بوقت صلاة رسول الله ﷺ للعشاء كان يصليها بعد سقوط القمر في الليلة الثالثة من أول الشهر
Its chain of transmission is sahih. Habib bin Salim is trustworthy, his hadith appears in Muslim, and he is the freedman of Numan. Abu Bishr Jafar bin Iyas is trustworthy and firmly reliable. The hadith was narrated by Abu Dawud 1/114, no. 419, Tirmidhi 1/306, no. 165, Nasai 1/264, no. 528, Darimi 1/298, no. 1211, and Tayalisi 1/72, no. 292, Minhah.