Hi. First I'm very glad to see a foreign person who is looking for sth related to Iranian culture. I will explain the answer shortly in Persian and then I will try to translate this in English. همانطور که می دانید سیمرغ پرنده ای است افسانه ای که ورود آن به ادب ایرانی همواره همایون بوده و سبب خیر است. در شاهنامه فردوسی ((سیمرغ )) به عنوان پرنده ای نام برده شده که از دستان(پدر رستم) مراقبت کرده و در تنگناها به یاری رستم می شتابد. این پرنده ی همایون در اشعار ایرانی نیز آمده، مثلا خیام در منطق الطیر(مقامات الطیور) حکایت چند پرنده را مطرح می کند که به قصد زیارت سیمرغ به راه افتاده و پس از گذشتن از موانع بسیار در نهایت تنها سی مرغ( سی پرنده) باقی می مانند و این می تواند به نوعی اتحاد و خلوص را در ادبیات و شاید عرفان نشان دهد به طور کلی ((سیمرغ را دیدن)) می تواند نشانی از سعادت و تعبیری خوش برای رویاها و خواب های انسان نیز باشد.اما من اصطلاح یا ضرب المثلی با این مفهوم در پارسی ندیده ام. As you know Simurgh is a mythical bird in Iranian culture. Simurgh always comes with being lucky and it causes good results for every thing. In Shahname of Ferdowsi, this bird raised Dastan(Rustam's father). It helped to Rustam (A great Iranian hero) especially in a battel between Iran and Turan, Simurgh helped Rustam to be alive again! In Manteq-al-Teyr(Maghamat-al-Toyour) of Khayyam (Iranian poet) There are several birds (Murgh) who want to see Simurgh, so they went to a dangerous way to see Simurgh. At last only 30 Murgh(birds) remained and they realized that they themselves are Simurgh.(beacuse in Persian language Thirty means Si). So, Simurgh can be a symboll of Incarnation or being pure in ideas in this poem. In addition if you dream Simurgh, it means you will reach what you want and you will achieve good results. But as I know, we don't have an exact expression for this in spoken and written Persian or even in Sufi literature. I wish this helps you. Sorry for my mistakes in translation.

It is not a real bird , it is a concept about best moral meaning that everyone should have them, simorgh has various meaning becuase a lot of poet have utilized this word in thier poems

Hi nata you want to know the word of it or the sentence of it ?!

It's not common in everyday Farsi at all, but the bird represents luck.

Nowadays if we want to say some wishes which we could not acheive them we say ( mahal : محال )