Musnad Ahmad 961:64

Al-Hakam ibn Nafi’ narrated to us, Ibn ‘Ayyash narrated to us, from Buhayr ibn Sa’d, from Khalid ibn Ma’dan, from Malik ibn Yukhamir, from Mu’adh ibn Jabal, from the Prophet, peace and blessings of Allah be upon him, that he said: "Whoever fights in the way of Allah for the duration of a she-camel’s milking, Paradise becomes mandatory for him." And a she-camel’s milking (*fuwaq naqah*) is the amount of time it takes for its milk to flow for the one who milks it.