From Sahih Muslim (Hadith 2105):
Asma' said:I came to 'A'isha when the people were standing (in prayer) and she was also praying. I said: What is this excitement of the people for? And the rest of the hadith was narrated like one, (narrated above). 'Urwa said: Do not say Kasafat-ush-Shamsu, but say Khasafat-ush-Shamsu
Reference: Muslim 2105