1. This Hadith has already appeared earlier [Hadith No 701]. "These are the ideas which come up in their minds" means that sometimes something appears and one's mind at once takes it as a bad omen. This is something instinctive and natural and one is not accountable for it. But if one acts in accordance with that omen then what he does is wrong and is, therefore, forbidden. For this reason, the Prophet (PBUH) said, "(i.e., these things) should not prevent them from pursuing their works."
2. The drawing of a line mentioned in this Hadith is different from the drawing of lines in 'Iyafah mentioned earlier. Moreover, that was an act of a Prophet which was done by him in the light of Wahy sent to him by Allah and, therefore, was certainly correct. But now, nobody possesses that knowledge and cannot, therefore, be adopted. The statement of the Prophet (PBUH) that: "The line which agrees with the line drawn by that Prophet would be correct" was by way of elucidation. It does not mean that that act can also be done by anyone today, for how can it be done without knowing its principles. How did that Prophet of Allah draw that line? What were its principles? Since that knowledge has passed away with that Prophet, it is now no longer valid, nor would it be fruitful.
Who was the Prophet who did it? Some people say it was Prophet Daniyal (Daniel), while other think it was Prophet Idris. Allah Alone knows the truth.