What is reference of hadith,whose approximate meaning/interpretation is as follow:
whoever prays isha and fajr in congregation (jamaat), he has earned reward of qayaam ul lail?
The most closest narration is that of:
'Uthman b. 'Affan (narrated the mosque after evening prayer and sat alone. I also sat alone with him, so he said: 0, son of my brother, I heard the Messenger of Allah (ﷺ) say: He who observed the 'Isha' prayer in congregation, it was as if he prayed up to midnight, and he who prayed the morning prayer in congregation, it was as if he prayed the whole night.
(Sahih Muslim which appears in similar words in Jami' at-Tirmidhi)
Where "morning prayer" refers to Fajr or Subh prayer.
The meaning and lesson learnt from this narration is that praying in congregation -in general and especially for the given two Fard prayers- is highly rewarded. This is highlighted in many other ahadith such as the hadith which you may find for example in Sahih Muslim:
The most burdensome prayers for the hypocrites are the night prayer and the morning prayer. If they were to know the blessings they have in store, they would have come to them, even though crawling, and I thought that I should order the prayer to be commenced and command a person to lead people in prayer, and I should then go along with some persons having a fagot of fuel with them to the people who have not attended the prayer (in congregation) and would burn their houses with fire.
Where night prayer refers to 'Isha' and morning prayer refers to Fajr/Subh as explained earlier.
And another lesson is that praying the night prayer is only optional as you may get its reward if you prayed 'Isha' and Fajr/Subh in a congregation.