It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Noble Prophet (peace and blessings be upon him) prayed two rak‘ahs after ‘Asr because he had not been able to pray any (Sunnah or Nafl) prayer after the Zuhr prayer.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الأوقات التى ينهى عن صلاة التطوع فيهن / 1276