Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said: If the fasts are missed, he should keep them after the days of Tashriq.
(b) It is reported from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he will fast during the days of Tashriq if he has missed the fasting.
(c) It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he will fast while in the state of ihram.
The hadith of Ibn Umar and Aishah is mawsul (connected), while the hadith of Muhammad bin Ali from Ali is munqati' (its chain is broken). And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8902