Ibn al-Musayyib (may Allah have mercy on him) said: The Sunnah has been established that in qasamah fifty men swear fifty oaths; if even one of them withdraws, they are not given (the right to) the blood.
This is munqati' (broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسامة / 16444