Musannaf Ibn Abi Shayba 35:120

Hafs narrated to us, from Hajjaj, from Abd al-Malik ibn al-Mughira al-Ta'ifi, from Abd al-Rahman ibn al-Baylamani, who said: The Prophet, peace and blessings of Allah be upon him, delivered a sermon and said: "Marry off the unmarried among you." A man stood up to him and said: "O Messenger of Allah, what are the ties (dowry/obligations) between them?" He said: "What their families agree upon."