It has been made permissible for you the night preceding fasting to go to your wives [for sexual relations]. They are clothing for you and you are clothing for them. Allah knows that you used to deceive yourselves, so He accepted your repentance and forgave you. So now, have relations with them and seek that which Allah has decreed for you. And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the sunset. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits [set by] Allah , so do not approach them. Thus does Allah make clear His ordinances to the people that they may become righteous.
Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (sallallaahu alayhi wa sallam) said, "When a man dies, his deeds come to an end, except for three: A continuous charity, knowledge by which people derive benefit, pious son who prays for him."
[Sahiih Muslim Hadiith No. 1631]
Seek what He has decreed for you means a child. This is the opinion of Abu Hurairah (may Allaah be pleased with him), Ibn Abbaas (may Allaah be pleased with him), 'Anas (may Allaah be pleased with him), shariih al-Qaadi, Mujaahid, al-Suddi, zaid bin 'aslam, al-hakam bin 'utbah, muqaatil bin hayyaan, 'ikramah, sa'iid bin jubair, 'Ataa, al-rabii' bin 'Anas, al-Hasan al-Basri, al-Dahhaak, and Qataadah. 
 Tafsiir Ibn Kathiir Volume 1 Page 512