It is narrated from Ata (may Allah have mercy on him) that Sayyiduna Ibn Abbas (may Allah be pleased with him) used to instruct that after the obligatory prayer, if one intends to offer voluntary prayers, then one should change place or speak, and then offer the voluntary or Sunnah prayers. Ata (may Allah have mercy on him) says that Ibn Abbas (may Allah be pleased with him) narrated a hadith: "When any of you has offered the obligatory prayer and then wishes to offer something after it, he should not do so until he moves a little forward or engages in conversation."
Hadith Referenceالسنن المأثورة / باب ما جاء في الأذان / 282
Hadith Takhrijمصنف عبدالرزاق : 416/2 ، سنن الكبرى للبيهقي : 191/2 ، سنن ابی داؤد، رقم الحدیث: 2133، وقال الالبانی: صحیح