Zaid lives in Saudi Arabia and he fasted with Saudi Arabia, but in the last few days he came to Pakistan. According to Saudi Arabia, his 30 days of fasting are over.
So should he observe Eid according to Saudi Arabia or should he observe the 31st fast in Pakistan?
Please provide references from fiqh books
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
If one completes thirty days of fasting in the month of Ramadhaan, and thereafter travels to another country, he/she will keep the fast in that country even though it sums up to thirty-one days of fasting. 
And Allah Ta’āla Knows Best
Mufti Muhammad I.V Patel
Checked and Approved by
Mufti Nabeel Valli
Darul Iftaa Mahmudiyyah
احسن الفتاویٰ جلد ٤ صفحہ ٤٣٣
فتاویٰ عثمانی جلد ٢صفحہ١٧٦