There is some narration from Prophet Muhammad (PBUH) installed in Masjid an Nabawi in Madinah, justified as "Sahih"(=Correct) or "Hassan"(=Well) in different Sunni references:
النَّبِيِّ صلى الله عليه وسلم قَالَ : " شَفَاعَتِي لأَهْلِ الْكَبَائِرِ مِنْ أُمَّتِي "
What is the idea of Sunni brothers about "Shafa'ah"? Who can do "Shafa'ah"? Is it Shirk to ask prophet's Shafa'ah?