A Jewish man from the people of Hira asked me, "Which of the two terms did Musa complete?"I replied, "I do not know, but I will go to the scholar of the Arabs and ask him."So I traveled and asked Ibn Abbas, who said, "He completed the longer and the better of the two. When the Messenger of Allah ﷺ said something, he did it."
سألني يهودي من أهل الحيرة: أي الأجلين قضى موسى؟ قلت: لا أدري حتى أقدم على حبر العرب فأسأله، فقدمت، فسألت ابن عباس فقال: قضى أكثرهما وأطيبهما إن رسول الله ﷺ إذا قال فعل.
Bukhari related it in the Book of Testimonies (2684), from Muhammad bin Abdul-Rahim, who said, Saeed bin Sulayman told us, Marwan bin Shuja narrated to us, from Salim al-Aftas, from Saeed bin Jubayr, who mentioned it.This statement that Ibn Abbas mentioned was not from his own reasoning, rather it has also come as a marfu narration. Perhaps he spoke of it in two separate sittings.