Allâh's Messenger (ﷺ) sent me for some job and when I had finished it I returned and came to the Prophet (ﷺ) and greeted him but he did not return my greeting. So I felt so sorry that only Allâh knows it and I said to myself, 'Perhaps Allâh's Messenger (ﷺ) is angry because I did not come quickly, 'then again I greeted him but he did not reply. I felt even more sorry than I did the first time. Again I greeted him and he returned the greeting and said, The thing which prevented me from returning the greeting was that I was offering the (prayer). And at that time he was on his (mount) and his face was not towards the Qiblah. [2:308-0.B.]