Abd al-Rahman bin al-Baylamani (may Allah have mercy on him) says that the Messenger of Allah (peace and blessings be upon him) said: "Marry off your widows." They said: For how much dowry (mahr)? He said: "Whatever their families agree upon among themselves."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14375