ubiquitin: see SA Siman 117 which discusses this issue.
http://www.hebrewbooks.org/pdfpager.aspx?req=49623&st=&pgnum=280&hilite=
http://www.hebrewbooks.org/pdfpager.aspx?req=49623&st=&pgnum=281 (see the Biur Halacha Divrei hamaschil UMIHU
http://www.hebrewbooks.org/pdfpager.aspx?req=49623&st=&pgnum=282