Hajjaj bin Amr bin Ghaziyyah (may Allah be pleased with him) was sitting with Sayyiduna Zayd bin Thabit (may Allah be pleased with him) when Ibn Fahd, a man from Yemen, came and said (to Zayd): "O Abu Sa'id, I have slave girls; the wives I keep are not more pleasing to me than they are, and I do not like all of them to become pregnant by me. Should I practise 'azl?" Zayd (may Allah be pleased with him) said: "O Hajjaj, give him a fatwa." Hajjaj said: "May Allah forgive you, we sit with you only to learn." He said: "Give him a fatwa." Hajjaj said: I said: "She is your tillage [Surah al-Baqarah: 223]; if you wish, water it, or if you wish, keep it thirsty." Hajjaj said: I used to hear that from Zayd (may Allah be pleased with him), and he said: "He has spoken the truth."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14319