Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) narrates: We were with the Messenger of Allah (peace and blessings be upon him) when a woman offered herself to the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) lowered his gaze and raised it, but he (peace and blessings be upon him) did not intend (to marry) her. Then a man from among the Companions said: "O Messenger of Allah (peace and blessings be upon him), marry her to me." He (peace and blessings be upon him) said: "Do you have anything?" He said: "O Messenger of Allah (peace and blessings be upon him), I have nothing." He (peace and blessings be upon him) asked: "Not even an iron ring?" He said: "Not even an iron ring, but I will divide my cloak into two parts and give her half." He (peace and blessings be upon him) said: "Do you know any Qur'an?" He said: "Yes." He (peace and blessings be upon him) said: "Go! I have married her to you in return for that Qur'an (that is, teach it to her)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13834