Muhammad bin Muslim (may Allah have mercy on him) said: The Messenger of Allah (peace and blessings be upon him) stayed fifteen days in Makkah, shortening the prayer, and then went on to Hunayn.
This is the correct (version), and it is mursal; Abdah bin Sulayman, Ahmad bin Khalid al-Wahbi and Salamah bin al-Fadl also narrated it from Ibn Ishaq and did not mention Ibn Abbas in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5469