Section 40(1)(b) in The Central Goods and Services Tax Rules, 2017
(b)[ the registered person shall within a period of thirty days from the date of becoming eligible to avail the input tax credit under sub-section (1) of section 18, or within such further period as may be extended by the Commissioner by a notification in this behalf, shall make a declaration, electronically, on the common portal in FORM GST ITC-01 to the effect that he is eligible to avail the input tax credit as aforesaid: [Substituted by Notification No. G.S.R. 1023(E), dated 17.8.2017 (w.e.f. 19.6.2017).]