Imām Ja'far ibn Muhammad al-Sādiq (alayhi salām) said
"Do not teach this amal [A'amal Umme Dawood] to each and everyone lest some should perform it for illegitimate purpose. It contains Great Name of Allāh (Isme Azam) and every desire will be attained for which it is performed in spite of all hurdles, even if doors of heaven and earth are shut as it were, Allāh will suffice even if all the mankind and genie are against the performer and every body will be subjugated. If performed, in any other month other than Rajab, in the middle of the month after observing fast on 13th, 14th and 15th it will carry the same benefit. It is also beneficial to perform this amal on any auspicious day like Friday or Arfa without observing fast".
[Reference: Mafatih al Jinan]