Sayyiduna Abu Sa'id (may Allah be pleased with him) said: 'Azl was mentioned before the Prophet (peace and blessings be upon him). The narrator said: He (peace and blessings be upon him) said: "What is that with you?" They said: "A man dislikes having intercourse with his wife during the period she is nursing, lest she become pregnant; or he has a slave girl and also dislikes her becoming pregnant." He (peace and blessings be upon him) said: "There is no harm upon you if you do not do it, for this is only the decree of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14312