Ubaydullah bin Abdullah reports from Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) "stayed fifteen days in the year of the Conquest of Makkah, shortening the prayer, and then went on to Hunayn."
He narrated it thus, but I do not consider it mahfuz (preserved).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5468