Sahl ibn Ziyad narrated from Muhammad ibn Sinan from Ibn Muskan from Abu Basir who said: I asked Him عليه السلام about a man who forgot Dhuhr until the time of Asr entered. Imam عليه السلام said: "He should begin with the obligatory prayer. Likewise with the other prayers, begin with the one that was missed, unless you fear that the time for the current prayer will expire, then you should begin with the one whose time you are currently in, and afterwards make up the one you missed."